You may also try home depot, lowes and Academy. The depot and lowes may have them in stainless steel because they are used for tieing wire fence together. Academy may have them because they stock some smoking supplies.
I got mine from LEMS and have both the 1/2" and 3/8". The 1/2 I find to be a little loose and the 3/8 are hard to get around the casing but fit good when squeezed. So I take the 3/8 and open them up with 2 pairs of needle nose pliers first and that works great. I'm doing this by myself so if you have a helper to get a tight twist on the casing you may get by without spreading. Good luck and happy stuffing !