Can anyone help me get hold of some airsoft parts or resin casts of shotgun parts?

I'm putting together a Pulse Rifle and have got a lot of the parts together but am struggling to get hold of the parts that go together for the Grenade launcher. Unfortunately you can't buy airsoft guns in the UK unless you have been a registered player for a certain period so buying the guns and cannibalising the parts is very difficult.

If anyone can get me the receiver for a Remington 870 in either an airsoft form or if anyone can make me a cast that would be great!

Thanks in advance for your help!