If they are in your budget I would recommend Triode Labs-Finale Audio (sister companies). They specialize in SET’s and have options, upgraded parts like transformers, IE Hashimoto etc. They are based out of Toronto and have been building SETS for over a decade. I've owned a 300B amo and 2A3 SETS from them and they are some of the best amps I've heard.
Not sure if you will find a balanced SET as that’s not part of the circuit design. They are from my understanding single ended designs.

