I ran into that myself when planning my own wedding. I had 6 weeks to pull it off, and every place I called thought I was calling for that date the next year! I found a restaurant with a banquet room that worked for us.
If you've already exhausted those options, get creative in your thinking:
Check out the locations belonging to local fraternal organizations (Elks, Moose, VFW, Masons, Grange, etc.), your parks and recreation district, or local colleges and universities for venues.
Do you know of anybody who lives in an apartment/condo complex or housing development with their own community center?
How about your local YM/YWCA?
Check out local museums or private mansions who may rent out their space.
Getting desperate? What about a school gymnasium or cafeteria? You can work wonders with decorations and pipe/drape panels.
Hope this gives you some ideas. Good luck!
Marti Barton, Officiant