i just bought a 89 cr250 but i need a new cylinder and cant find anyone out there that has one.

you could always bore and sleeve your current cylinder, then use a chromed ring set. That's what I did with my CR250r I had back in the day.

wont the sleeve wear out quicker than the cylinder?

the factory set up was a cast ring and niksil or chrome cylinder. When you install a sleeve, you basically reverse it, going to a chrome ring on a cast cylinder. My bike would go 2 riding seasons on one piston/ring set after the sleeve job, where before I was replacing them every season.