You're not going to save a lot of money shopping online but www.grainger.com carries a ton of plumbing, electric, and other industrial items. Get 1/4 turn ball valves.
I'd also to with regular sweat valves, you're not making anything easier using threaded valves. You would still need to un-sweat the pipe from the male adapter or cut the pipe to change the valve since trying to loosten one end would just tighten the other. All using the IPS valves is going to do is cost a few dollars more in labor and materials.