Actually from my experience with it, they don't care; movie/tv productions use replicas, including rubber guns, non firing replicas, model guns (including airsoft), squib guns and blank firing guns... squibs and blanks aside (blanks require an armorer on set, squibs require a licensed pyrotechnician at least), they're all considered "replica props" and aren't illegal per se (they're illegal to display in public without the proper permit).
Also the CFC isn't in the loop here. Actually I dont think the CFC is ever in the loop, they're non authoritive. Since its being shot in the city he needs municipal permits. The one for guns needs to go past law enforcement whom, as mentioned before, will most likely come around. Since its being shot downtown, its very likely they'd have to close off the sector to the public. Since you have a shoestring budget, things aren't looking too good for you. Sorry.