The other option for taking the AFOQT/TBAS is to find somewhere that will let you take it. As was mentioned ROTC units sometimes have availability, but being a Marine, you do have access to bases, and the AFOQT is often available on bases that you can just call and sign up for. I seem to remember a website that listed all of the different testing locations for the AFOQT and TBAS. I took the AFOQT at Randolph and the TBAS at the ROTC Det at University of North Texas. I set them both up by myself because my recruiter was useless, and I was majorly crunched for time.
In terms of pilot selection, it is similar to the Marine Corps, in that the Marine Corps will guarantee a flying slot before you leave for OCS. The Air Force assigns all jobs before going to OTS, but the Marine Corps only assigns pilots.