Bill & Martin,
You need to be aware that amidol is pretty toxic. Also, it turns your fingers/fingernails black. I was going to say "beautiful black" but I didn't know if it would be seen as the joke I meant. Brett Weston's hands were pretty strange looking. He used both it for prints and pyro for film, I believe. The pyro stains the hands, too. I use pyro, but I'm not willing to risk the amidol, thanks.
I suspect that sodium carbonate must be available in Brazil. If you can't find the carbonate, I would seriously doubt that you are going to find amidol anyway. Sodium carbonate is a very common chemical. Amidol is definitely not common. Sodium carbonate comes in three forms, the anhydrous, the monohydrated, and the crystal. If you are mixing developer from scratch, it is very important to know which one you are usling. Check the formula, and research it if necessary because the formulas often do not say which to use. It will make a difference.
In its anhydrous form, sodium carbonate is also called "soda ash" in English, but I have no idea what it would be called in Portuguese. I get it at a well stocked art supply store (MUCH less expensive than buying it at a photo store!) where it is sold as a mordant for dying fabrics. If you find "Procion" dyes, you will most likely find it as well. I keep it in a "ziplock" freezer bag, and it keeps just fine. I use it in most of my developers and it works perfectly.
Most common is the "monohydrate" form. Both the anhydrous and the crystal (which I doubt that you will find) tend to become the monohydrate over time unless you take reasonable care to protect the anhydrous from absorbing moisture. The crystal gives up its moisture. If using the monohydrated form, you need to use 17% more than you would if using anhydrous. If by some chance you end up using the crystal, you need to use three times as much as you would using anhydrous.
Low grade sodium carbonate (which would probably work) is called "washing soda" in the US; it used to be available in grocery stores, but now I think it can only be found in hardware stores. If you find some, it may have had some scent added, which I know I wouldn't like very much. I am fairly sure that it would be the monohydrate, but don't hold me responsible if it turns out not to be! It might be "unknown".
If I were having trouble finding it, I'd call the local university chemistry department and ask someone there what it might be called and in what forms it might be available in its less pure, and less expensive grades. You do not need high quality such as "reagent" grade. "Technical" would be entirely adequate. "Technical" and "photographic" are about the same.
I don't know if you can still find Kodalk. Kodak seems to still be making some chemicals, but given their current direction toward discontinuation of silver based products, I don't trust them, so I tend to stay away from their proprietary formulas. However, I'm grateful for your advice, Bill, because I have about ten pounds of it I didn't know what I was going to do with. I'll just cook something up.
Another tricky thing to do would be to leave the carbonate out, put in an excess of sodium sulphite, and add about 30ml of acetone to your tray. Not really critical. This dissociates sodium sulphite and produces sodium hydroxide. I'm not sure how much sulphite you'd have to add, and if you experiment with it, be sure to keep your hands out of the tray because it will be more alkaline than is good for our skin.
A substitute for Sodium Carbonate (monohydrate) is Sodium Metaborate (also known as Balanced Alkali or Kodalk). Use only .59 as much as the formula calls for carbonate.
Another option is to compound formulas based on the developing agent Di-Aminophenol (also known as Amidol). Such developers contain only Amidol, Sodium Sulfite, and Potassium Bromide. For Paper, choose Kodak D-51, Ilford ID-22, or GAF 113.
Amidol is also excellent for film development. Since there is no alkali present to soften the emulsion, processing can be safely conducted at temperatures up to 85 degrees F.
Ilford ID-9 is a good choice for such tropical development.