What's up with winged c 6550's?

For some reason the winged C 6550's seem to have disappeared off
the market for the moment! Since everyone tells me that these are the tubes recommended by ARC,I am looking to get five of them for my ARC D70.

They seem to be as rare as pixie dust now, with everybody out of stock and
not sure of when new stock will arrive or if they will arrive at all.
Anybody know what's going on? Better tube suggestions for the ARC?
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Not sure if this website are updated, but here we go

Mamad and Btstrg, Thanks for the help. Apparently, the tubestore.com has these tubes. Ctech has a few BUT no singles...