I'd like to thank everyone who gave me suggestions.

It turns out that there _is_ a brand that will let you switch Caps Lock
and Control.  As Ted Lemon and Jim Bernard pointed out, Keytronic
(http://www.keytronic.com) makes the KB101 Plus, which has this feature.
This is still being produced, and I have ordered one via one of the
mail-order superstores.

Thanks again!

--Ken