Enjoyed reading about the various tube rolling adventures and choices of tubes. Regarding the Mullard tubes the CV4010 and M8100 are supposed to be very similar - the main thing is to get tubes made in the UK in the Mitcham factory, which was supposed to be one of the most advanced of its time.
There is another Mullard tube which is very similar and sounds great: EF95/CV850.
Lastly, to add some more challenges to the tube rolling, I never paid more than $8/tube (including shipping), and usually less than half of that. The trick is to check Ebay often and to communicate with the seller. You want to deal with the guy that does it as a hobby and is selling off his grandfather's stock or stuff he got at an estate sale; not the people who do it as a business and charge you $89.99 each for the same 6AJ5 tube that I just picked up for less than $6/pair.