Pistol shrimp and shrimpgobies are pretty common, so most online retailers should have them. If you want specific recommendations, you could try any of the sponsors of this forum:
https://www.reef2reef.com/categories/sponsors.5/
The best option, albeit a fairly expensive one, would probably be someone like Dr Reefs. Someone who fully quarantines all their livestock, so you don't have to worry about disease or about starting your own quarantine tanks.
Though you might have to hold off on buying online for awhile, as it's pretty hot. Maybe wait until September or October. And try not to buy anything time-sensitive from mid-November to mid-January; the mail tends to be prone to bad delays and lost packages then, with all the Christmas shopping. Corals via overnight shipping can be risked, since they'll last a few days in transit, but fish and any mobile inverts (shrimp, etc) should absolutely not be ordered online during peak Christmas shipping season.
