never heard of it,but that doesn't mean we couldn't try .
i think you should start with chicken or poultry stock,or vegetable stock since you want to use it with fish aswell.
Sautee some mirepoix in vegetable oil,add a bouquet garni,bayleaf ,garlic,crushed white peppercorns,pour in the stock,bring to the boil and leave to simmer for 30 minutes,pass trough a fine sieve and season with salt.
roast the schezuan pepper ,put in a peppermill and add to the sauce when you serve it.
You can always add cream or thicken the sauce.
this should be a nice basic try-out.
Speaking from my european point of view that is.....
I run an exhibition saute line at an upscale corporate cafeteria in Foster City, CA. The menu changes daily, and pan asian foods are the most popular for my station.
To make a perfect szechuan sauce, start with an overly spicy base.
Saute your szechuan peppercorns in sesame oil. They will soften. Add balsamic vinegar, samboulek chili sauce, brown sugar, and oyster sauce. Simmer and let reduce to thicken after 10 minutes. Add a base appropriate for the protein such as chicken, then add apporpriate volume of water for base used. Add oyster sauce, soy sauce, and sherry wine. Simmer and thicken with cornstarch if needed.
Saute your chicken, and veggies (Chinese long cut beans, celery, carrot, bell peppers), add hydrated rice noodles and toss with the premade sauce.