Upgrade the indicated weapon fully to unlock the corresponding bonus weapon for purchase from the shop.

Gatling gun for Chris: Fully upgrade the VZ61.
Hydra triple barrel shotgun: Fully upgrade the Ithaca M37.
Longbow for Sheva: Fully upgrade the S75.
M93R pistol (Samurai Edge Custom): Fully upgrade the M92F.
Smith and Wesson M500 Magnum (Handcannon): Fully upgrade the Smith and Wesson M29 Magnum.