Reliable source for 6550WE tube - Audio Research Ref 6

Re-tubing an ARC Ref 6 and seems like the 6550WE tube is hard to come by these days. Upscale only sells to Primaluna owners, Tube Depot has it on backorder. 
The only other source for this tube that I was able to find is The Tube Store. Any comments on quality of their tubes?

Also, thinking to replace the Sovtek 6H30 with EH 6H30 Gold Pin tubes.
Thoughts?
 

Thanks in advance!