Oh, the already-roasted ducks! I thought you meant raw uncooked "Pekin ducks" (no "g")...
I suspect you also mean the "Cantonese-style" roast ducks, then, rather than Peking Duck, which is something slightly different? The ducks one sees hanging ubiquitously in shopfronts in Chinese restaurants (at least in Manhattan's Chinatown) are NOT really Peking Ducks, which would have shatteringly crisp skin separated from the body, served in a specific way. The ones "just hanging around" are commonly simply "燒鴨" (Cantonese Yale: siu1 ngaap3); whereas actual Peking Duck "北京烤鴨" (bak1 ging1 haau1 ngaap3) usually needs to be a special order. (Except, of course, in places that specialize in that - such as in certain restaurants in Beijing itself :-) where the ducks would be cranked out in a steady stream)
Don't many of the restaurants still make their own? I know at least some of them did some years ago - one could ask nicely? (I had also seen some of them carrying out hot, steaming ducks from the BOH to the front "kiosk" in years past, at times when I happened to be there...the one at the corner of Mott & Bayard, for instance - but that shop is gone, I think, so that is of zero help to you. Sorry.)
Hope others will pipe up.
