i wana bring the front sight back to the gasblock chop re thread and crown the barrel. is there any gunsmiths in vancouver someone can suggest??
So to answer the original question:
You don't want to do this yourself for legal reasons, and gunsmith that doesn't have manufacturing license will refuse to do it for legal reasons as well.
Thus you need to get in touch with someone who has manufacturing license, document what modifications you want on the barrel, and agree with the manufacturer what barrel you want manufacturer to manufacture for you. At this point you will know if the manufacturer wants your existing barrel as one of the consumables for the re-manufacturing, or if they can make you a new barrel from scratch.
Once you have tentative agreement with the manufacturer (always make agreements with the "provided that RCMP/CFC deems the part legal" or similar clause), call up CFC, and ask to talk to the gun technician. You will be transferred to the gun lab in Ottawa (extension 1090). Explain to the person who picks up what you want to do, and confirm that the barrel manufactured by the manufacturer that you made an agreement with will be legal. If you really want to cover your bases, ask for a written statement.
Once you know what RCMP/CFC wants, and as long as what they want, what you want and what the manufacturer can do all align, call the manufacturer back, and go ahead with the process (ship him the barrel if necessary).
Eventually you will receive back a new barrel, hopefully to your spec, and some paperwork.
With paperwork you got in hand, call up CFC, and once again ask to talk to the gun lab. Explain to them the situation, and offer to fax them the paperwork from the manufacturer. Once they get your paperwork, they will create a new FRT# for your firearm, and amend your registration. You will potentially get a new registration certificate for the firearm.
Do not install the barrel before calling CFC, though. This is in case something goes wrong and your new barrel gets ruled to be a prohibited part - while the barrel is not installed, you don't have a prohibited firearm, so alot less legal trouble.
Yeah, if RCMP challenges "newly manufactured"-ness of your new barrel, you'd have a receiver only CZ-858, but think about this way: A competent lawyer charges about $200/hr (cheap lawyer). Your CZ-858 costs $750 new. Do you think that 4 hours of work by the lawyer will be enough to get RCMP off your case? So don't install the barrel until you get all clear from CFC. In fact, you'd likely need to take the barrel to a gunsmith, who will be able to verify to the CFC the length, etc of the new barrel.
I'd suspect that you can start by e-mailing or calling Dlask, North Eastern Arms and Rauch Tactical, and see if these fine manufacturers will be able to do what you want.