I don't think that most local fish markets shuck clams. The shucked clams likely come in giant bucket/jar from a packing plant, but you could certainly ask. You can buy shells for cooking from a restaurant supply store, but they are not cheap (something like 4 for $5, or $150 for your 120 shells). If you want to make this recipe, you may have to open and clean the shells yourself.

Don't you also need the clams? Can't you ask a fish market to sell you 120 clams, and to shuck them for you and give you both the meat and the shells?

I probably will need about 120 or so to make clams casino but don't have time to do it myself. I've callee a couple of fish markets who do not sell the clam shells. Any ideas where I can get some? Thanks!!