Attack on Titan

This achievement is a really long grind to upgrade and buy every equipment you need to 100% the gallery. Coming from someone who did this all single player, I wanted to share enough information to help others, so people wouldn't have to search among other forums and sites to find how to obtain and/or where to obtain a single item. As stated in the other solution about doing the TAM (True Attack Mode) Survey missions and Requests net you a lot of money, that some of the items I won't bother mentioning if you can simple buy them.

In case you want to find some items I don't list, I came across this website that ended helping quite a bit on where to start looking for some items, then figuring out which mission gave the most and/or fastest way to obtain an item I needed.
https://aot-wof.herokuapp.com/en

Now I am not sure how multiplayer goes for farming items with Sasha, but I literally use Levi 95% of the time because majority of the time when I used Sasha, she would obtain about the same amount of an item as I would obtain with Levi, but took longer and struggled more with her as she does not put out as much damage as Levi. With Levi you can chain up to 6 hits which is helpful in certain situations or you can do massive damage 1 hits with his spinning attacks. On top of that you are able to throw your broken blades which give another opportunity to do damage.

For main equipment that you want to use, Try and figure out which blade/scabbard/ODM gear you want to use. Try to upgrade or buy those as soon as possible and fortify into them when you complete other fully upgraded equipment.
For myself I ended with:
(Blade) Cloud Zero Plus / (Scabbard) Perfected Scabbard / (ODM) Camellia Zero Plus

As far as weapons go, I want to note that these weapons you need to buy multiple of as they split upgrade into other weapons otherwise I would buy at least one of every weapon when you get the chance. If you happen to buy duplicates, do not sell them, but fortify them into the weapon you want to main.

Blades
Reinforced Blade Ver.1 -> First Daybreak
Tiger Zero -> Cloud Zero
Rapier (Buy 2 extra) -> Unicorn Horn / Nightmare Blade

Scabbards/Canisters
Reinforced Scabbard Ver.1 -> First Daybreak
Swifthorse Zero -> Wave Zero
Wing (Buy 2 extra) -> Unicorn Crest / Nightmare Sheath

Omni-directional Mobility Gear
Reinforced Gear Ver.1 -> First Daybreak
Panther Tail Zero -> Camellia Zero
Symbol (Buy 2 extra) -> Unicorn Tail / Nightmare Heart

Here is a list and my input on the items that you need to farm as you cannot buy them.

Ultra-hardened Crystal Fragment 'Sasha'
'Normal' Attack Mode / Wall Perimeter Secure Area: The Second Plan to Regain the Front
These are gained from the Muscle Titans and this mission is good to farm for this item as this mission you are able to farm out Rare Metal as well, which you need quite a bit for Symbols and Wings. One of the few missions I used Sasha for.

Large Ultra-hardened crystal 'Levi'
TAM / Eastern Region 2nd Survey Area: High-Firepower Area
To me I felt this was the fastest way to farm this item. I used Levi for this because I was running this mission in about 5 mins compared to Sasha struggling with 10 min completion and still getting about the same amount. You get these off the Muscle Titans and there are 3, sometimes 4 of these guys depending on what the first red "!" spawns. I obtain 0-5 per run. This is the hardest item to grind out because of the low if any at all mission outcome.

Large Titan Armor Fragment 'Levi'
TAM / Eastern Region 2nd Survey Area: All Men, Move Out!
Instead of heading straight to the red "!", I went North to the green "!" that Mikasa is at. There is only 1 Titan there to kill for her to be recruited and she is a S-Rank ally which is helpful. Also completing a side task instantly fills your Decisive Battle Signal which helps on tackling the Armor Titan. From here I would go to the red "!" and kill the 2 random Titans near (they can get in the way) before taking on the Armor Titan himself. I was normally able to obtain 2-4 each run.

Ominous Titan Crystal / Glowing Titan Crystal 'Levi'
TAM / Choices and Consequences (story mission)
Ominous Crystal is obtained off the Beast Titan and the Glowing Titan Crystal is obtained off the Female Titans. Simply in the first part of the mission, kill of the Female Titans legs as they are easy to target and hit. The annoying thing Female Titans do when you latch onto their arms is snap your hook on them and offset your targeting. In the second part of the mission if you knocked her legs off in under 2 mins, The Beast Titan will show up. Go to him and use your fire bombs to rid of the defense cover on his legs and only destroy his legs for the item farming. You don't need to kill him. I would not worry so much about farming the Glowing Titan Crystals as much because you will need to farm this mission enough times to get the amount Ominous Titan Crystals you need.

Large Titan Crystal 'Sasha'
TAM / Eastern Region 2nd Survey Area: Titan Encirclement
This was the mission I need to use Sasha. At this point in TAM, any Survey Mission that is at least 7 star rating, should be able to net you Large Titan Crystals off ANY Titan limb you cut off, but this was the mission was I able to farm the most out of. Obtaining up to 26 in a single run.

Superior Gem Steel 'Levi'
'Normal' Attack Mode / Soldiers Dance (story mission)
Though you are able to buy this item, you end up needing it quite a lot and running this mission nets you 3 every time and when you are upgraded enough, this mission becomes real fast to run through.

Colossal Crystal 'Levi'
TAM / Last Line of Defense (story mission)
You can only obtain this item from the Colossal Titan and only on TAM. This item becomes a little annoying to farm as when you complete this mission, you get pushed back at the Main Menu screen of the game. Doing this mission on Normal nets you the Unusual Titan Crystal.