Almost all gyms have a "one time visit" option or even a pass for the whole week, but if you're looking to find other people to play with, I would suggest trying a YMCA in your area first. The people who play there on a regular basis would know of more places to play, tournaments, etc.

Or you could google gyms in OKC with racquetball courts and try the ones close to where you live....no gym is gonna make you pay a full membership upfront, though.