I thought somebody else with more knowledge would jump in...
I ordered gallic acid from a store which supplies teaching materials for schools, also for chemical experiments. You might try to locate such a store in the area where you live.
I suppose you read Alan Greene's book?
I once tried gallic acid as a developer for prints (not negatives!), but my experiments came to naught, and I left them there, getting interested in other processes.
My best advice is: don't try to get around this one ingredient. Such old recipies are generally difficult enough to bring to life, and trying to substitute one ingredient for another is likely to make your experiments very frustrating.
By the way, should you succeed with your endeavour, i'd like to see a print...