Ruokangas has released a pickup with a built in tube. It requires its own pedal to power the tube and active electronics.
So, who’s going to be the early adopter? Could be a cool project if you’re willing to drill a giant round hole in the middle of you bass.
I’m guessing they will build one for you with the Valvebucker in it, but I couldn’t find the pricing or build option on their website.
Edit: I found some information (guitarplayer.com) saying they only sell it as part of a new bass order. I don’t know how much the bass will cost but the Valvebucker pickup system, by itself, costs $2000 to $2200.