Here are some of the suppliers I've used, in alphabetical order:
- Art Craft -- This is one of three dedicated photochemical suppliers I've used. They've got a good selection, although not quite as good as Photographer's Formulary, and moderate prices.
- B&H -- The general photography superstore offers some photochemicals, mostly from Photographer's Formulary.
- Digital Truth -- This site is the smallest of the three dedicated photochemical supply sources. (They seem to be branching out and selling film and other stuff, too.) Their prices are fairly good.
- The Chemistry Store -- This site has general-purpose chemicals for hobbyists. They lack some vital photochemicals, like metol and phenidone, but they've got excellent prices on other items you're likely to need in bulk, such as sodium sulfite and sodium thiosulfate. Their shipping charges tend to be a little high, though.
- Local supermarkets, etc. -- You can find sodium carbonate (as Arm & Hammer Washing Soda), ascorbic acid (vitamin C powder), and a few other items in local stores. You can save a lot on shipping by buying locally, but see below....
- Photographer's Formulary -- This is the premiere dedicated photochemical source. They've got higher prices than some competitors, but a bigger selection.
- Summer Bee Meadow -- This outfit is dedicated to soap making. I mention it because they're a good source for sodium hydroxide and potassium hydroxide, which many other places refuse to ship.
I recommend you start with just one or two suppliers, if possible. Buying from several will just drive up shipping costs, eliminating any savings on the items themselves.
One extra comment: If you buy from a dedicated photochemical supplier, the chemicals you get ought to be of suitable purity for use in photochemistry. This might not be true of other sources, so be aware that there's a risk. That said, I've used items from all these sources (including supermarket sodium carbonate, several items from The Chemistry Store, and potassium hydroxide from Summer Bee Meadow) with no obvious problems in the results I get. Overall, I'd say that using such sources is reasonably safe for hobbyist purposes, but there is some risk. When using extremely oddball sources, such as supermarket items, research them extra before using them. (Note that the iodine in table salt can cause problems in some photochemical formulas, so you should definitely
not use iodized salt for formulas that call for sodium chloride.)