Tube rolling newbie- how to choose NOS tubes

Google Brent Jessee or Vintage Tube Services. Both are respected tube sellers who will help you find the tubes you want. They probably will not be cheap , but who knows, you may get lucky. Buying tubes from these guys is not cheap but it is cheaper than learning about NOS tubes by trial and error.  Brent will usually get the tubes to you faster than Andy (VTS).

As petg60 has recommended, get familiar with the sound of your DAC/amp with the stock tubes in it and have an idea of how you would like to change that sound with your new tubes before calling the tube sellers..

Brent Jessee +1

+1 for Brent Jesse his advice is top notch and his return policy is more than fair. Basically you pay for shipping and get to try something else within 30 days no risk.

But definitely let the stock tubes break in if the DAC is new and get used to them as others have said.

Many of the reissues are mediocre, some are good for the specific application (JJ comes to mind).  

You will learn a lot and get pricing from his web site here: audiotubes.com/12au7.htm

Emailing him is best, explain what you have and what you are looking for. Don't get stuck on Mullards though (nothing against them, I have a pair in my DAC from Brent that I love but they were $450 a pair) but there are other great NOS options that might be obtained for less.

Not sure what the rest of your system is but there is a point of diminishing return to consider.

+1 Brent Jesse

+ whatever on Brent Jessee.

@kennyc  here is the link to his website, if you click on the specific tube type you are interested in a page will come up with impressions on different brands and equivalent tube models

I haven't used Vintage Tube Services , but as noted by another member he gets good reviews. Another option is TubeDepot