No and no. They do not count towards the achievement and the only way to get them is with a save from the first game. They are only bonus weapons and really aren't worth the money because you can't customize them and they are kinda bad compared to other weapons you could use.
Best fully customized weapon IMO is the G36C.
If you wanted them you could just launch the first game and start the first mission (without getting any achievements) and quit, launch The 40th Day, get the weapons, then delete the first one's saves.
The first Ao2 is so much better but impossible to finish now thanks to Electronic Asshats.
I have moved to PC gaming, so I
won't be on Xbox LIVE anymore.