I have about 8 or 10 different types of materials and sized meshes for painting. I've always done better buying in person than online. I found them at all the places you mentioned, had the best luck at a large fabric store, just have to keep looking until you find what you want. I think LPO carries two standard sizes, I've found both at fabric stores for a quarter of the price. I have found very, very small mesh for a Roman made repaint at Walmart, they also had several other different sizes as well. I have found other materials that worked such as- mesh bags that garlic or oranges come in, bath luffa or i've even used the mesh bag my boat cover came in, it had real big holes.
I know this isn't the answer you're looking for but you just have to keep looking until you find that specific size. I have a large container of meshes to choose from now. Hope you find what you're looking for!