Verlinden did lots of resin weapons, often with photoetched cradles. They are out of production, but should be all over ebay.
Some of their stuff is a mishmash of eras and features and some was overscale.
Legends makes resin guns, .50 for sure but these may be more modern.
Another option depending on your comfort with photoetch would be Eduard etch sets for the given vehicle. These often have PE additions to the kit gun, but require filing or carving off molded on details. Their website www.eduard.cz has PDF's of the instruction sheets you can check ahead of time.
There are a couple of dedicated injection plastic gun sets, but those are are not really my jam.