200 psi is usually fine, we don't swing hard enough in nero to worry about that. There's PVC and CPVC, either should work for one handed weapons.
Part of your difficulty might be the inflection. You're not looking for 'wall foam', you're looking for 'pipe foam' with 3/4" wall. The 'wall' designation lets them know that the measurement that follows it is relating to the thickness of the foam (the wall of the foam) rather then the diameter of the pipe you're putting into it. Most of the time, the foam will have printed on it something like '3/4" ID 3/4" Wall.' ID stands for Inner Diameter, which isn't really the inner diameter of the foam, but the Inner Diameter of the size of pipe that is generally used in it. I generally buy 3/4-3/4.
Pacific Plumbing Supply also carries the proper type of foam in Washington, but they're a little pricier.
There's a couple things that you can do for open cell foam. I generally go to Fred Meyer and buy a camp mattress, which'll run you about $13, but will set you up for open cell foam for life. If you're not looking to make a bazillion weapons like I am, you can go to Joanne's Fabrics, and they generally have huge sheets that they'll cut a chunk for you. It's more expensive per quantity, but you won't buy nearly as much. At joeanne's it's generally white or green. If someone happens to be throwing out a couch, rip open one of the cushions, usually there's open cell foam in there.