I don't think you'll get many takers for an exchange that happens every month. You might be able to find an individual or two who will do a "pen-pal" type of reciprocal exchange - you send them a photo, they send you a photo. But I wouldn't count on that always being once a month. Sometimes, it's hard to find time to get into the darkroom to make a print - particularly one you might want to send to someone else.
So, I think you should try the postcard exchange. You'll find most participants are in the US. You don't have to use "postcards" - you can make a print (as small as 3.5x5 or as big as 5x7) and put it in an envelope.
It is good practice and you will get some swell prints in return.