Centre is less common than theatre, but I've seen it in many places. It's usually around plazas or shopping centres. If we pull in the Constitution, we should using -our and -ce spellings. The Constitution uses "behaviour" and "offence" and "defence".
How is any of that relevant? The Constitution was written BEFORE American English had standardized spelling.
Also, the spelling "centre" is extremely rare in the United States. The fact that you have "seen it in many places" is shocking.
Or standardised, even.
In the U.S., I usually see "centre" in places like subdivisions or strip malls that are trying to be cute with their names, similar to "olde" and "towne". (There's one in my area with the trifecta; it's actually called "Olde Towne Centre".)