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.

I did a search one at Brent Jessee’s site and came up with this:
You'll need to scroll down a bit to see what he has in stock.

Good luck and all the best,
FWIW I read somewhere that the reissue Gold Lion KT88's had a similar tone. My SED6550's are still working so I haven't tried them (yet?).  Also, as an alternative in another amp to the SED 6550's I've been using Tungsol 6550's. The are a tad warmer than the SED's in that amp. The Tungsols are probably less linear than the SED's but they are rugged and not at all expensive (compared to NOS SED 6550, or anything else made by SED for that matter.) 
I just bought some Gold Lion KT88s for my Prima Luna. A very nice sounding tube. 
Replacement for SED 6550C Winged C

I had great results with Rogue M120 monoblocks, modded with far better output transformers with KT90’s then after KT120’s from Mike Mathew’s New York company "New Sensor" or "Electro-Harmonix" Whatever he calls it today. Just make sure the heater circuit is up to it, as from memory I think one or the other may take a bit more current than the 6550.

Even cheaper with an account.

Cheers George

As for the best sounding 6550 I’ve listened to, it been NOS Mil Spec Green Label GE plain white box, like these $350usd each!!!!!
The glass was twice as thick you feel it in the weight and hear it when you flicked them with your finger nail.

Cheers George
I switched from SED 6550C Winged "C" to Gold Lion-KT-88's for my VTL amps many years ago.  They are a bit warmer with better bass. I enjoy them so much I've not considered trying another brand of tube.
Also use NOS JAN GE 6550. Winged C 6550 do come up from time to time from US Resellers. 
The SED Winged C 6550 (c I believe) made in St. Petersburg is my favorite tube, but I was unable to find a quad that worked.  I purchased a quad from a US vendor and they each red-plated to one degree or another.  The vendor replaced them, but the second quad did the same thing and I received a full refund.

I gave up on the Winged C and tried a set of Psvane KT88-TII. I like them enough that I am sticking with them, but I would buy a set of Winged C in a heartbeat if I could find a good set.