"I wouldn't piss on you if you were on fire"

[fluxrad]

If everyone knows you're a regular, including the manager then the solution is easy: Call the manager, ask to know the nights that waitress B is not working and let him know that those are the nights he can have your business.

Even if he doesn't tell you when she's working (no manager in his right mind would divulge that information) he'll at least know that waitress B is starting to cost him money in terms of visits from regulars.