Armslist.com
guns america, and like web based stores, then all you need is a local shop to be willing to accept and do paperwork when it gets there
shouldmn't be hard to find, they made a TON of them combo's over the yrs
it might also be cheaper to just buy a used gun of each too?
there very common shotguns and used and in good shape shouldn't be hard to find
NEW 870'S can be had at big chain stores on sale for under 250
just check weekly flyers for likes, of cabela's, Bass pro, gander MT, DIcks, DUnham's and so on/
even wally world