I've got a few lav mics that aren't wireless, all I can do is plug them directly into a mini recorder which is what I've been doing. Can I buy wireless transmitters/recievers separately and attach them to what I already have rather than buy a whole other set of lavs separately? Thanks, anyone.

Chances are you'll have to rewire them to use a particular wireless transmitter's connector.

While it's not a tremendously difficult process, it does require having the information on which wire connects to which pin, having the right connectors (the ones used for Lectro and AT systems can't be found at Radio Shack), and some soldering skills.