Current Marketplace for Vacuum Tubes?

Hang on to those tubes!  Tubes will be here forever. Quickly obsoleting the more affordable transistor amplifiers and gear. Only six figure solid state can compete.  Brand new tubes are being made, so you don't have to worry about NOS tube supplies running out(unless you prefer them). Personally, I like VTL(Vacuum Tube Logic) gear. Rock on!

Listed tubes on US Audio Mart, AudioAsylum, and a few on E-Bay.

Thought I’d follow up now that I have marketed and sold a dozen pairs of vintage tubes.

Audiogon ads received little action, rendering the cost of a basic ad plus photo at $9 a poor value. I spent $45 on ads for items that didn’t sell (and received no offers).

I sold two pairs of tubes on E-Bay. The cost of listing, final value fee and Paypal fee at an aggregate of about 11% is another relatively poor value.

The remainder of the tubes were sold via AudioAsylum Trader or USAudiomart. Considering both those marketplaces cost nothing to post ads, and one can accept several forms of payment, including Paypal "Friends and Family", they are the current go-to venues, IMO.

I'm glad that you were able to off-load some of your old tube stock Grant. 

I concur with your findings. I do almost all of my selling on AudioAsylum Trader and USAudiomart the last couple of years.
I buy there too, though I still buy some things on AudiogoN. 
I do not use Ebay to buy or sell audio equipment.