I'd talk to your instructor and see if he/she knows of any openings.
Another option is to open the phone book and create a list of places to apply (private companies or the hospitals if they run the local service), get your resume and brag book ready, then head out and apply.
Not as familiar with the SD area as up here in LA, but I know Rural/Metro handles the EMS for SDFD...though I think they're mostly if not all medics. Don't know which other companies operate down there, but I'd assume AMR has a presence. Asking your instructor's a good place to start.