I have searched McMaster-Carr without finding anything. Maybe this is a special made part but I doubt it.
The next four pictures are the clamps on a couple of my saws. Click them to enlarge. I get a lot of questions about blade slippage and about the knobs. I wanted to talk for a minute about these subjects. The pictures are from my Excalibur and one of my DeWalt DW788's
I have in the past shown how to make or buy larger knobs for the thumbscrew. The thumbscrews can be hard on those with weak or sore hands. The above damage can be caused by the extra torque you can gain from the larger knob or lever. That's why I always give the warning that you want to be careful with the larger knob. Just use modest pressure. If the blade is slipping you need maintenance not more torque.
These tips can apply to other scroll saws as well depending on how their clamps work.
Keep the set screws and thumb screws maintained.
Make sure they are adjusted so the blade rides centered in the chuck.
Do not over tighten the thumb screw. If the blade is slipping check these tips.
If you sand the tips, do it gently. Don't remove material. Just lightly rough up the tips. Get a replacement set when needed. They are not that expensive when you consider the aggravation of slipping blades.
A little removable Loctite on the left set screw can help keep it in place.