Almost all SURPS, SURFs, REUs, etc. are for future PhD students. Your best bet for finding research opps for future MDs would be to find ones affiliated with medical centers and/or teaching hospitals. It might take some time, but do a ton of Google searches with "xyz medical center research opportunity" or something similar.
I don't think anyone has published a list of MD only research opps yet, although I'm sure there are some folks on sdn who've gone through the trouble of making one.