I'm waiting for my PaRodinal to finish maturing, but I need stop and fixer.
The parodinal should be ready for use in a day or two, so that should be about done.
For stop bath, you can use for instance citric acid, which is commonly sold in drugstores, shops that sell winemaking supplies and perhaps even some food stores/supermarkets. Alternatively, use acetic acid which is commonly available in the form of cleaning vinegar (ca. 8% acetic acid). Various other acids would work, too, and you could even simply use a water rinse instead of a stop bath especially when developing film.
Fixer is a bit of a different story; in practice, it's usually the most sensible to just purchase ready-made photographic (rapid) fixer. If you insist on brewing your own because of a lack of supply of photographic fixer (although surely, there are still other analog photographers active in Mexico), you could try and find sodium thiosulfate in a store that sells swimming pool supplies. Sodium thiosulfate is used to reduce the chlorine level in pools. Sodium thiosulfate will make an old-style non-rapid fixer; it will not be the best choice for modern t-grain films (Kodak Tmax, Ilford Delta, Fuji Neopan; you will need to fix these for a very long time), but it'll work OK for other films and paper.
If you want to make your own rapid fixer, you could either use sodium thiosulfate and add ammonium chloride; there are formulas for this online. Ammonium chloride may be a little more difficult to buy from food stores etc.; again, check brewers/winemakers stores. Another way to make a rapid fixer is to get hold of some ammonium thiosulfate. This is sometimes sold as a 60% solution intended to be used as a plant fertilizer; it's sold as "ATS" and "12-0-0" fertilizer. If you find any fertilizers by that name, verify in the accompanying documentation that they are indeed 60% ammonium thiosulfate. The dry material isn't commonly sold since it's very hygroscopic.
Sodium sulfite is often used as a preservative in fixer; again, check winemaking supplies stores; they often sell sodium sulfite as well as sodium metabisulfite. Sulfite is also available from stores that sell food supplements since it's a commonly used preservative. Since you've already made parodinal, you apparently have managed to find sulfite, so that's a good sign.
As you can see, many of the chemicals used in photography also have other uses, and this means they can be obtained from a variety of sources. There are of course some chemicals that are less commonly used; the developing agents like phenidone, hydroquinone and metol are good examples. For these, you will have to look at specialized firms that retail chemistry for lab use, or platforms like eBay (esp. for small quantities).
Personally I purchase most of my chemistry online with retailers in the food, winemaking etc. business or sometimes retailers specializing in arts suppliers and art conservation. I only rarely order from "chemicals suppliers" as such, since they're generally not very consumer-friendly, place emphasis on larger quantities and especially the big brands tend to be rather expensive.
Hope this helps!
