Pawlowski6132,
Are you asking about vintage NOS PX-25's? Osram, Marconi, etc. PX-25 are available from tube collector/dealers, but they start at ~$1,000 a pair and go up up to $2,000 or more(?).
But, as I said in my first post, there are 3 current companies manufacturing PX's right now: KR, Sophia, and TJ. These cost about $500-550 a pair new.
NOS PX-25's can cost just as much as vintage Western Electric 300B's or some really nice vintage 845's. Maybe just a little less. I don't relly know because they are so far out my comfort zone, financially.
If you've got connections in England, it might be possible to find NOS PX-25's cheaper, but then shipping and spec matching becomes a real concern. For the money, all the new production are fantastic.