In putting together my grav and melta dev squads, I ended up with a lot of extra heavy weapons. I'll trade any two for one grav gun, or I'll take $5 for each.

4x Lascannons (2x old style 2x new style )
4x Plasma Cannons (2x old 2x new)
7x Missile Launchers (1x old 6x new)
6x Heavy Bolters (all new)
1x Multi-melta (old)

I also have other random odds and ends from the dev kits. If you have anything you're looking for, like the creepy ammo cherub because everyone wants a creepy ammo cherub, ask me and make an offer.