Thanks for the reference to the references, Jack. I emailed them, and
got back a nice reply that said, in summary:
-- Yes, they sell singles, no problem.
-- Order direct from them.
-- Current prices for four items I asked about are
** VRE100C $43.50 4 week lead time
** VRE102C $48.73 in stock
** VRE302AS/AD $11.04 in stock
** VRE302CS/CD $6.52 in stock

Those first ones are extremely low tempco parts (typ. 0.3ppm/C) with
very good initial accuracy (0.01% max error), +10V and +/-10V. The
second two are 2V parts with still very good tempco and good initial
accuracy. See their website for details.

Cheers,
Tom