I'm sure I saw a 350 tank in this exact colour on Ebay the other day.. Its hard to get exact colours unless you find NOS tins of Honda paint. Or your other option (especially when its a metallic or candy colour like alot of these late 60s / early 70s Hondas were) is something like House of Kolor which as we all know ain't cheap..
I like these SL350 tanks for vintage scrambler builds and even CB track bikes to save on weight, and they're always (well at the moment anyway!) still affordable.