Replacement for SED 6550C Winged C

 I am now using SED 6550C winged C from 2008.  I really love the tone texture of these tubes.

I am having some trouble with my set (4) of these tubes and would like to get a replacement, however I am not finding the exact replacement, made in St. Petersburg, at a reasonable price from a trustworthy dealer.  I could get a set from  Russia but I prefer to try domestically first.

Consequently, I am asking if any of you, having experience with this tube, if you know of another tube that has such tone and texture.  I focus primarily on vocals.