I have a foursome and I really like it. The pistols I got as a pair from someone, but Peter S recently posted info on sexing the pistols.
I doubt you will be able to find a pair in a LFS. I have occasionally seen them in the process of pairing up in LFS' though. In a community tank, they will often lay across each other in an "x." Or I have had LFS employees point out two that they think have paired up, since they know I have a pair. They get to see the fish together so they have a better idea than you can get on first glance.
They aren't hard to pair, it's just that you may or may not get a pair, and you need to have a separate tank to remove the rejected fish to, if need be.