Sig Store, Top Gun Supply, Midway USA, Brownells, Midwest Gun Works are but a few.
You can always just buy a complete parts kit to get the roll pins: SIG P226 9mm PARTS KIT - $23.99 - Top Gun Supply These are definitely worth having.
You can also use the spiral roll pins. I use them in my P6:
Sig Sauer Firing Pin Positioning Pin - Current P Series - SPIRAL - $7.95 - Top Gun Supply