Not to far OT. 300b anyway. Doc if you haven't tried the Brimar 300b's they might be approachable for a sample pair.
Last Sunday I went to the bi-annual Audiojumble at Tonbridge, Kent here in the UK. A large table was occupied by Brimar
http://brimaruk.com/ Noted that a large box packed with their brand of 300b. Website says £179 for a very close matched pair. Reasonable?
Lots of "old" and established Hi Fi notables there with stalls inc Ken Kessler and the like. I bought the Sansui QSD-" decoder that was tested by Hi-Fi News back in 1972(?) marked as "sample" and with Ivor Humpreys (sp) on the box. Why? Don't ask.
A click around the links at the top of this page
http://www.audiojumble.co.uk/should keep you entertained for quite a while. Especially this one.
http://www.audiojumble.co.uk/previousevents.htm