Thanks very much, bregez -- that helps. I realized one reason I couldn't source those parts through Newark is that I'm ordering through their Canadian site -- for some reason they don't stock them, though the US site seems to. I can find the diodes I need at Mouser, too, I think.
While I wait for the printed circuit board to arrive I've been scrounging through my parts box. Found a couple of very nice unused (now discontinued) Hovland MusiCaps (1.0 uf, 400 v) that might work as output couplers, if they fit.