A couple options that i can think of. First, if you can create your own "month" navigation that creates a URL parameter (say ?date=201602), then you can have the calendar display events within that month via macros and the WHERE condition, and use the same macro to modify your repeater.
Or you would possibly have to clone the Calendar webpart and have it set a macro in the API that the other tool can grab (see the MacroContext class). If you need to do this, i can try to provide more code.