Not what you want but I have extended the original barrel to make it longer and comply. I drilled out the original rifling and put in a barrel liner then rechambered (semi-auto). I was also changing the bore size (calibre) from 32 and 25 to 22. I have done this twice. The guns were inspected by the RCMP in Ottawa.
The liner is smaller in diameter than the extended portion. I added an extra piece over the liner to increase the diameter so it it is about the same diameter as the original barrel doesn't look so dumb.