Unfortunately this is not possible unless we're talking about Electro-Harmonix, Sovtek, Ei or JJ tubes. Even then I'm not sure whether it would be possible. Those are the only brands which are still being manufactured.
All the other tube manufacturers have ceased production and therefore there is a finite amount of vintage 6DJ8 series vacuum tubes left of the planet.
Due to the laws of supply and demand all we would possibly be successful in doing is raising the price for all future buyers of vintage 6DJ8 tubes. Therefore, the only companies that could possibly be approached for a group buy are the ones listed above. Anything from Telefunken, Amperex, Siemens, Sylvania etc. are vintage and have a stable valuation which cannot be changed via mass purchases.