You might want to check out any forum or advice that comes from Maple Tree Audio. The guy that builds the amps Pre and Integrated uses 12SN7s.
Other than that I think you'll find that many of the better 12SN7s are a lot like their 6 volt counterparts. For instance I had and gifted a friend some NOS Tung Sol round plate 12SN7s which are a lot like the 6 volt tubes but easier to get and much less expensive.
I would try older Sylvania, the Tung Sols and RCA, to start. You might want to ask over on Tube Asylum of the Audio Asylums as well.
Other than that I think you'll find that many of the better 12SN7s are a lot like their 6 volt counterparts. For instance I had and gifted a friend some NOS Tung Sol round plate 12SN7s which are a lot like the 6 volt tubes but easier to get and much less expensive.
I would try older Sylvania, the Tung Sols and RCA, to start. You might want to ask over on Tube Asylum of the Audio Asylums as well.