I have for sale one matched quad of JAN Sylvania 6BQ5. These tubes are the dark shiny black plates with green lettering 90-90-91-87 in their original JAN boxes. $150 plus shipping.
I also have another NOS quad of Sylvania 6BQ5 with the same shiny black plates with three having yellow print and one having green print; two in white boxes and two in the original yellow and black Sylvania boxes. These were supposedly matched but there is only test data on one tube. $125 plus shipping.
EDIT: I also found a pair of NOS GE gray plate 6BQ5's in their original boxes. $55 plus shipping.
These tubes seem to be very rugged and long lasting and sound excellent. My first quad has been going strong for six years now.
You can contact me here on Audio Circle if interested.