Unfortunately I think it's not easy to get the fresh ones here, even from the wet markets. Coming from Japan I am also a huge seafood lover (clams and mussels especially) but sadly, I don't get them much here. Sometimes I will go to the wet market and buy 1-2 kg of mussels but hey, a few bad ones in there would spoil the whole pot... I have tried tapping and I have also asked the sellers to select the "good ones" for me but the results have not been satisfying at all.
The best way to do it is to, after soaking them in the salt water for about 5-10 min, "smell" all of them one by one. The one that gives you the "fishy" smell is the one that you need to separate from the rest... (if you hate to just throw it away). If it gives a "stench" smell, throw away immediately.
It takes lots of effort to have fresh and great mussels/clams here...but it's worthwhile if you are the seafood lover
