I can vouch for the eBay seller known as "widebasket" from S. Korea. He is very prompt, and he packs items expertly.
As for the Leopold keycaps not fitting on at least some boards with Costar stabilizers, I have not yet tried them on such boards. I really like the Leopold caps, and I have put them on a CM Novatouch with no issues. However, I plan to get a WASD V2 87 key keyboard; I hope that the Leopold keycaps will fit, because the WASD uses Costar-type stabilizers. If not, I would be in the market for other PBT keycaps, preferably with dye-sublimated legends.