Festool makes some.
(Amazon.com product link shortened)
They're either called screw clamps or F clamps.
Festool sells them they're also available from Amazon.
I bought the ones I have because my confidence in the stability of the guide
rail for the Festool Plunge saw had not yet been established. ;-)
I bought a few Jorgenson clamps at an estate sale a year or so ago
that are similar, and would certainly do that job. Don't know if they
are still available but your might watch sales, flea markets, etc. I
don't remember what I paid but it wasn't more than a buck or so each.
At the same sale I bought a full-up Jorgenson bench clamp for $30.
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