Tube vendors.

Brent @ AudioTubes. Great deals on NOS, but some are not so NOS but given the pricing, ridiculously good value.

eBay but ya gots to know what you're doing.

Matching is a bit of a shell game. The tubes are seldom run and matched under real world conditions which vary mightily between amplifiers. A match at one point may not at another.

For a well matched set, they should be run for several hours before matching.

Amplified Parts doesn’t have a single mention of matching as related to tubes on their website, so quite possibly are selling sets matched by the original tube vendor.