You're not getting a custom spec anything from mercury magnetics, made to Bogner's specifications, without being a Bogner certified repair center of which there are few and far between.
Sounds to me like you need to sell the amplifier. When you can't get the tone you want and need to start changing transformers, one of the most expensive items installed, it's time to sell for something that is closer to your end goal.
I don't know why people either think transformers are the first thing to go wrong in an amplifier, or the most dominant tone source in the signal chain. It's a part of the pie like everything else and IMO you're going to get less of a tone change going from high-quality OT to high-quality OT than going from garbage OT to high-quality OT. It's not as drastic as you believe and the details are only more apparent at band volumes and after hundreds of hours of playing.
