Here's an idea, fold the sleves inward and fasten them with pins. Then bring the jackets with the pins in place to your local tailor. Without a doubt I am sure he will know exactly what you want done. Or just say "quiero acortar las mangas de este saco por "X" centimetros" - I think this will be much easier than looking around for an english speaking tailor. Tailoring unfortunately is becoming a lost art and those that are around will tend to be older gentlemen. Just a suggestion on my part.......good luck.
A few years back, I had some shirts altered by some Russian ladies who have a small shop on Independencia and Piedras (on the N. side of Indpendencia, just a little beyond Piedras towards the W.) I think that the shop is still open. Jim Mattea