Excuse my dyslexia: amp TUBES for my Crack Speedball.
There are a couple of sources, but eBay is really the big one.
I've spent a small fortune on tubes for my Crack + SB, and while the setup I have now is worth the gain, the amount of money would ideally be better spent towards a better amp.
Sometimes ignorance is bliss, tube gambling just to see how one might sound over the other is pretty addictive.
if I were in your shoes I would hold off on tube rolling / any other modifications, enjoy what you have, and when you can afford it or have the itch, upgrade to one of Bottlehead's higher end offerings.
If you are set on tube rolling, try to acquire a Tung-Sol 5998, and a CV4003 from Mullard or Brimar (that is what I'm running, and is my favorite combination, and the most recommended for this amp).
Additionally, in my experience, paying a premium from specialized dealers versus eBay sellers has been worth it.