The reason why you're having problems finding used tires is because cars don't come with 14s anymore. I had 14s on my old Cutlass. I didn't drive it much so when I blew a tire I said screw it and tried to buy used. They just aren't out there. I work at a dealership so we have tons of used tires. Still couldn't find any. The fact is manufacturers are running 16s and up on nearly every car now. 14s are a thing of the past. You could try a place like Bob Lee's. I believe he sells used tires.