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.....
Szechuan sauce 
just get stirring 
I'll give it a try...... 
my dear Syneclise, I'm sorry but I thought you needed a Schezuan pepper sauce, hence the improvisation..... 
