Tom, W8JI hinted at the problem in his answer.
Let me very DIRECT.
DIY Projects for vacuum RF power tubes (glass and ceramic) that are no longer manufactured -- are really pointless, other than for educational reading.
Your local library can get ANY ARRL Handbook, on loan form other libraries. Many communities and all states have taxpayer supported libraries -- if not in your town, nearby -- in Montana the state university libraries have what you require -- FREE.
As far as DIY building a new RF tube HF amplifier -- AVOID glass tubes.
The 811A/572B tube still exists largely due tot eh audiophile market -- which buys more of these tubes than the amateur radio market.
The 3-500Z tube is only made in China and USA is capable -- but that production line is not being operated -- last I heard (low demand).
That leaves you with the Eimac and SED/Svetlana made ceramic RF power tubes.
RF Parts RF tubeshttp://www.rfparts.com/tubetran.html
Commercial amplifier builders have the SAME issues in deciding on parts availability (long term support) for building HF Amplifiers!
The PRICE of tubes has changed significantly in past 7 years. Russian surplus tubes (1980s mfg) have been cheap and plentiful (GI-7b triode) -- but the cheap price will not last forever.
I prefer using a Triode RF tube, such as: 8874, 3CX800A7 and 8877 tubes.
Prices have stabilized a bit -- due to 2 mfg. being available.
Tetrodes can be used -- BUT I highly recommend the usage of a control board (GM3SEK) for tetrode designs!
Parts for the experienced DIY builder / restorer:
Paul Hewitt, WD7S Productionshttp://home.earthlink.net/~wd7s/
GM3SEK Triode and Tetrode control boardshttp://www.ifwtech.co.uk/g3sek/
Once you select a TUBE, this leads to selecting the proper power/plate transformer design (windings for filament, grid, screen(tetrode), and plate).
Harbach Electronics/Peter Dahl have a wide selection.