A couple tubes I find among the absolute best in the 6dj8 family have not been mentioned.
Mullard 6922, gold pins. Excellent tube with great bass authority, and overall clarity, without excessive warmth and certainly not dry. Great tone. I was somewhat surprised by this tube as I often associate Mullard with overly warm and often thick sound.
Mazda 7308. Probably the most dynamic and snappy tube I've heard in this family. Nice tone, a bit sweet. Not warm, not bright. Really good top to bottom.
Other mentions:
Siemens CCa - Very even handed with very nice tone, but I find them a tad dull for my preference. They're very expensive. Sold my pair. I wonder how different Telefunken CCa would be. I've never tried.
Amperex 7308s - I dislike these quite a bit. I consistently find them overly warm, and too veiled. They lack the clarity of either the Mullard or the Mazda mentioned above.
Where to buy? Brent Jessee is my preferred tube dealer. He's a bit more expensive than others, but his service and consistent quality makes it worthwhile.