You can find 99.9% at amazon.... About 13 bux a liter.
Here's what I used 6 months ago when I made my first batch... And what I'll be using for the next one soon, since my stash is finally gone..... Sadness.
there was just another thread on this topic with some folks saying they found it at local nail/hair supply companies. I see that Grainger's also sells it but don't know if they regulate who they sell to. 99.8% about $50 gal.
Just got back from Frys in Renton, they had 2 types of 99.9% Iso, then one I linked earlier for 13 bux, and the stuff I bought that was only $9 for the same size, a litre.