To get good gouge on the USAF Guard and Reserves, you need to go to wantscheck and baseops, PPRUNE is focused on aviation mostly in Europe. Next, each guard unit does it's own hiring so you have to go to each unit's website to see if they are hiring UPT Candidates. You can also call up the officer recruiter OF EACH UNIT, and make sure it is the officer recruiter and not the normal recruiter. Ask if they have a mailing list for UPT candidate announcements or officer announcements.
Next, you need to get the paperwork rolling because it is a long process. You will need to take the AFOQT and TBAS so that you can also get a PCSM score, all of which you'll need. You will also need letters of recommendation. You will need three. If two are not from military officers, you will really be limiting yourself in the process.
Good luck