The time I tried patching a crack in the intake manifold with epoxy, it lasted all of maybe 15 minutes.
As far as picking up a good used one, just about any junk yard should have at least one Crown Vic/Grand Marquis/Towncar with a good intake. The U-Pull-It yard by me has many of them.
1997 Grand Marquis GS - Died
Now have a 2003 Grand Marquis LS