Risen

If you are going to do this, you most likely won't be able to do it in one playthrough anyway. It does track the amount of blades forged between savegames and playthroughs, so the easiest way to achieve this would be with a fair dose of saving and reloading. Now, forging is a time consuming process no matter what, but here's a quicker method than forging one sword at a time, and not using a single Speed spell!

Buy, steal, beg, or prospect your way to 10 sword blanks (8 iron ore per blank, traded in at every smith). Find a nice smithy somewhere, preferably at night so you can work undisturbed. Put your first blank to the forge and heat it. Instead of going for the Anvil next, hit [B] to put the glowing metal in your pocket. Ouch. Pull out another blank and continue doing this until you have 10 blanks through the fire. Continue to the anvil, hammering out 10 heated blades. Take your 10 glowing swords to the water trough one at a time. Keep hitting [B] to put them away. Now, SAVE. With 10 dull blades in your inventory, hit the Whetstone and voila, 10 Sharp Swords. Reload and repeat 10 times for 100 forged swords.