Email [log in to unmask]  They will do all kinds of custom and stock glass
components.  The glassmasters are NIST traceable and they call linear accuracy
of



±0.0001", with orthagonality of 1 arc second.

I used them to make a qualification board for my previous employer.  I bought a
variety of 4 parts with quantities ranging from 8 to 25, and believe I paid
somewhere between $50-150 per part.