The problem with banning replicas is "What constitutes a replica?"
Are airsoft weapons included? Many of these are plastic. Are kids toys replicas? Some look like the real thing.
Blank firers may be convertable but what about pure replicas that have no barrel as such?
It's a minefield as far as definition goes which may be why the government have held off with a ban (so far).
The fact is converting them is illegal so if they stop that illegal source another will be found.