I did another filter test last night with Canon 450D (FSM) and Canon FD 400mm f2.8 (@f4).
The combination performs very good IMO, with focussing with Bahtinov mask (the star to focus on should be G~F type.. I also tried with Betelgeuse but the Bahtinov pattern was somewhat ambiguous and resulting focus was a tad off... obviously the lens issue).
The uvir-cut filter comes from LenOpTec (Beijing, the contact person was Oswyn Tu,
info@lenoptec.com), the service was exceptionally good (they posted the item 2 days after receiving payment via PayPal).
Two filters plates 1.1mm thick (I asked them to cut it in round shape, 45mm dia, so I could mount the filter into Canon filter holder to replace "standard" neutral glass) cost me US$50.00 +US$25 for postage via TNT.
I imagine the other shapes and sizes are not the problem for them.
Compared to Hoya, Baader Planetarium and Astronomik prices for such filters, LenOpTec filters are absolute bargain... and the published data very closely match my own measurements.