Oh, and don't forget the plastic Space Marine Commander has a DW pad as well,a nd teh sprues for the Blood Angels Sanguinary guard has several (I think three or so)
Also, look at the latest things that Forgeworld is doing, their old-style bolters look the bizz and can easily be converted to Deathwatch bolters. Even normal plastic bolters are easilly converted, just replace the barrel with some plastic tubing, drill out the center and voila, a suppressed bolter.
For the heads I wouldn't worry too much, I'd say, go for any helmet, Personally I'm a big fan of the classic beakies and the MK5 ones that look like primitive beakies. I never was of a fan of the MK7 mouth-grille types.
And never forget Ebay if you're looking for that one specific little bit... they sell everything separate on there.