Far Cry Primal

A few tips:

Some of the rarer skins I managed to find by fast travelling between campsites near the animal in question and circling around with my owl. Keeping your hunter vision on will help you spot rare animal scent trails. If you don't see the beast after a few passes, rest to switch to day/night or fast travel to another camp near the beast and try again. (I also used this tactic to track down some rare tameable beasts).

Clays and reeds are typically nearer water. Probably goes without saying, but resources named North/South are typically found in the North/South of the map respectively.

Also bear in mind that your last two specialists won't appear until you have captured the major Izila/Udam forts, and won't have huts until you complete their initial village missions.

Just keep remembering to skin everything as you go, and pick up every stick and stone you see, and this should come along fairly naturally whilst going for everything else.

List of resources below. Note that you can't deposit items and you can only carry so much, so don't waste time trying to farm all the easy resources early - focus on keeping hold of the skins. You can always run around and top up slate, alder and reeds once everything else is in hand.

Takkar's hut:
Level 1:
4 Alder Wood, 3 Slate, 2 Reeds, 4 Goat Skins
Level 2:
35 Alder Wood, 25 Slate, 10 Reeds, 4 Badger Skins, 40 village population

Sayla's Hut:
Level 1:
4 Alder Wood, 3 Slate, 2 Reeds, 2 Deer Skins
Level 2:
35 Alder Wood, 20 Slate, 20 Reeds, 4 Mammoth Skins, 40 Village population

Tensay's hut:
Level 1:
2 Alder Wood, 2 Slate, 2 Reeds, 2 Wolf Skins
Level 2:
38 Alder Wood, 15 Slate, 16 Reeds, 1 Rare Black Lion Skin, 40 Village population

Wogah's hut:
Level 1:
3 Alder Wood, 3 Slate, 3 Reeds, 2 Jaguar Skins 
Level 2:
20 North Cedar, 15 North Black Rock, 10 North Clay, 3 Cave Bear Skins, 40 Village population

Jayma's hut:
Level 1:
5 Alder Wood, 4 Slate, 3 Reeds, 1 Brown Bear Skin
Level 2:
45 South Maple, 30 South Stone, 15 South Rock Dust, 2 Rare White Deer Skins, 40 Village population

Karoosh's hut:
Level 1:
4 Alder Wood, 5 Slate, 2 Reeds, 4 Wolf Skins
Level 2:
30 North Cedar, 35 North Black Rock, 20 North Clay, 1 Rare Stripe Wolf Skin, 40 Village population

Dah's hut:
Level 1:
15 North Cedar, 15 North Black Rock, 15 North Clay, 1 Rare Black Dhole Skin, 40 Village population
Level 2:
35 North Cedar, 25 North Black Rock, 20 North Clay, 1 Rare Two Horn Rhino Skin, 50 Village population

Roshani's hut
Level 1:
25 South Maple, 20 South Stone, 15 South Rock Dust, 2 Rare Red Elk Skins, 40 Village population
Level 2:
50 South Maple, 40 South Stone, 30 South Rock Dust, 2 Rare Red Bitefish Skins, 50 Village population  

Any mistakes spotted or tips to add, let me know in the comments.

Just wanted to add something to Kintaris' solution: Another way to get some of the rarer skins is to do the Beast Kill missions (one of the orange quests on the map). Once I started doing those regularly, the last few skins I needed for upgrades came pretty quickly.

Also, if you're having trouble finding a rare Bitefish, try this: Go to a lake on the map where they dwell (look for the character symbol), stand near the shore, and toss meat into the water. It will bring a bitefish in moments, and I got a rare one after just four kills of regular ones. I tried it again later and I had a rare bitefish in five kills.

Please let me know if this works or not so I can alter or delete the solution if needed. Good luck!