I don't see a way to get this information. Menus aren't "attached" to anything; they're displayed in a location. Your -menuForEvent: override might work but it gives me the willies.
While this isn't an answer to your question, I confess my first reaction is "why do you have multiple tables with exactly the same menu?" This strikes me more as a UI issue. One would think a contextual menu would be pretty specific to the specific kind of thing (or view thereof) that it represents. That begs the question: why do you have 5 table views that all have exactly the same context? If all 5 tables represent things that are controlled in the same way by the (presumably) same controller, it's highly likely there's a better way to represent your "collection of things" than 5 separate tables.
I'm making a lot of assumptions, granted, but my curiosity is getting the best of me, I suppose. :-)