Start calling around now to all the churches in the area. They are used to these kinds of calls and will not think it's odd. Their music dept. will have leads on harpists.
Call FSU's music department. They have a good string dept.
Or, if you don't need the visual of a harpist on the altar, you'd be amazed at the exact sounds a good keyboard can duplicate. Almost any string instrument can be duplicated and replace a musician out of a high paying job!
Check the classifieds too, lots of musicians are looking for gigs.
Also, be open to other stringed instruments. Most could replace a harp and would be much easier to find, again from FSU or local schools.
Good luck, and best wishes!