Reserve units can usually be found either in their recruiting stations, or, more likely, online. I know that the 20th SF Group, until they moved, used to do 6 month tours to central america building hospitals, airstrips, and the like. An army reserve unit would be a combat engineer unit. Although, they may or may not be able to handle your request (alot of em are cycling through Iraq constantly, and may not have the equipment/manpower to do it). Another option would be the us army corps of engineers. Or, even fundraising. I dont think that, normally, reserve units can just accept a job for "training". I was national guard infantry for 10 years, and, we DID do alot of security for the state, but, thats what we were there for. Good luck.