I don't know all the places to buy that type of sinker, but you can make some any size you want. Buy some oval slip sinkers, or standard bullet weights, or round slip sinkers in all the sizes you like to fish.
Get some SNAP swivels about the size you would fish with for trout.I don't know the sizes cause I just eye-ball it. Crimp the snap swivel end closed, or cut one side off. Insert the crimped end into the hole and push it in until you get to where the swivel ball is located. IF YOU PUSH IT IN TOO FAR THE SWIVEL WILL NOT SPIN. It's obvious !
You can tap it in with a piece of soft wood also. Next, take a pair of pliers or channel grips and squeeze the lead till you get a good crimp. You can crimp the top where the swivel enters, not the whole sinker and it will hold. If you don't want to change the shape by squeezing the sinker you can use 5 min. epoxy to glue it in, and that baby won't come out.

One of my buddies ties on the crimped swivel to his main line and just crimps a sinker on real lightly so that when he gets snagged the swivel comes out of the sinker. He puts just a little bend in the end so that it grabs a little bit. If you do this don't crimp the snap swivel, cut one side off so that you just have a straight piece of metal. It will look like a straight pin. This takes a little practice, and I don't have the patience!

You can use cheap swivels that don't spin as good, or buy some sampos. Good luck and remember to PRACTICE AND TEACH CATCH AND RELEASE !!!!!

BURGIE