In your achievement log, you can see which achievements get you mastery points. There's heaps of them. The only region that causes me some issues is core Tyria, as I still need 8 points for the last mastery, - but with other regions, HoT, PoF and the living world masteries, I never really ran into issues. I actually have too many PoF mastery points (would probably be enough to do all rollerbeetle masteries if I ever unlocked it).
Have you tried checking the open world masteries? If you have the basic mounts in PoF, you can reach many of them - and all you have to do is commune with them when you find them. They are marked on your map with a special sign. In addition to those, there are plenty that you can get with achievements, of which many can be quite fun!
By the way, I am just a "casual", so if I can do it, most people can. Don't give up :)