Straditubes.com
John Kim. KS Park collaborated with Kim over the last 5 years regarding the:
HL2, rs242, 3A and 300B.
This is a relatively new company but already has three versions of the 300B that perform. There are many great tube companies out there and some I especially respect.
Stradi has excellent customer service and I personally buy from them. (KA has no affiliation with them otherwise.)
Kron is another consideration.