Get a copy of the phone book. Doctors are listed by specialty. Often their training is listed. Those trained in the US or Canada will speak English. Often they will list other specialties or training that might be of interest to you.
According to Wikipedia "Custom-compounded BHRT is a practice almost wholly restricted to the United States.", so you might have trouble finding it in Mexico. I assume you are aware of the issues related to it so I won't belabor the point.
Gosh, that's surprising and disappointing. Actually, you can get it all over the world. I've gotten it at a top hospital in Thailand and also in France (besides the US). It's pretty much gone mainstream. Personally I don't believe in the scare stuff; that's been updated and certainly not considered the last word- I have done my research but not really interested in debating it so thanks for not going there. I believe I have seen it in other parts of Mexico but Mexico City is much more convenient for me these days.