Take a look at Bud's Police Supply
for a list of manufacturers who evidently have programs. Either the manufacturers or Bud's seem to limit the number of firearms sold as I have seen some models available for regular commercial sale but out of stock on the police side. I have a Colt AR on layaway there. Be careful about Dan Wesson 1911s there, however. I've actually seen them higher priced on the Police Supply site than on the regular commercial site -- if they're available at all.