Depends. You can get new old stock ($$$) to used old stock ($). General brands like Westinghouse and Sylvania are rebranded RCAs, RAYTHEONs, TUNG-SOLs etc.
Then there are Black Plates, Gray Plates, Short, Long etc. Enough to make your head swim. Then types and gain factors to add to the confusions.
I have the RCA Black Plate in my Vox amp but it has the gain factor of 70% of the 12ax7 so I have a couple of vintage 12ax7 tube on the list. I'm still looking around. I usually get my tubes at TC Tubes but I found a site called Viva Tubes which has better prices.
NOS NIB RAYTHEON JAPAN 12AX7A SHORT GRAY PLATE TOP SMALL O GET VACUUM TUBE 100+%
And
STRONG VINTAGE MULLARD BRITAIN 12AX7A ECC83 VACUUM TUBE ROUNDED PLATES LOW NOISE (branded as RCA)