I bought my last batch of Ascorbic acid (vit C) off ebay, believe it or not. Very cheap. From a chemical wholesaler in Germany, it is 100% pure. I've used quite a bit already and I've not had to compensate one bit.

If you have problems getting hold of Potassium Bromide (KBr) for your faster films, try out iodide/iodine enriched salt. Though not a topic in the Caffenol Cookbook, several of the authors have tried it out and posted their results on flickr.