There is a slight misconception about pellet choice for .20. It's true most shops don't stock much if any but if you look online, there's a decent selection to try. H and N, JSB, Daysate (which I think are pretty much identical to the JSBs), Logun, Dynamic, Benjamin and others. All quality makes.
It is very true that the gun selection can be a bit poor but if folks get in touch with dealers, manufaturers and importers and ask direct, many of them can accomodate