The Ken-Rad VT-231 or 6SN7 is becoming a rare bird. You can get them on Ebay from tubemanaus. These are from Australian military NOS. He usually sells a pair of these every couple of weeks and has a good supply. I bought a pair of Ken-Rad VT-231 and Sylvania VT-231 from him about six months ago and highly recommend him. I'll try and find a link for you with his contact information.
Here is a recently completed auction. I would try and sidestep the auction thing and see if he would sell to you directly. I think his minimum bid lately has been about $89.00 for these. Other brands of this tube can be bought here in the U.S. for less, but if you have your heart set on Ken-Rads and don't want to mess with questionable used tubes, he has the good stuff.http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1345763147