Your best bet is to purchased ORA Farm raised clams. Clams and shipping are always an issue, though probably not as much of a problem as shipping Xenia.
I, like you like to see what I'm getting, however many of the websites now selling livestock actually show you the piece you will be getting.
Purchasing anything online is a gamble, however shipping techniques have improved considerably over the recent years. If you see a Clam you like online, by all means buy it!!!!!!
Remember that Clams are very touchy and can perish if you don't acclimate them slowly regarding light, salinity and pH...
Good luck!!!!