Well, in NS, you get the Registry of Motor Vehicles to run the numbers. If they have no record (in other words it hasn't been registered for a long time) then you obtain a verification form from them and have a police officer confirm that the numbers you are trying to register are indeed the number on the machine. Then you take that form back to the Registry again, they give you an affidavit form where you declare where and how you got your hands on it...they ask you if the statement is true...you say yes, they stamp the affidavit and process your registration. I imagine it would be a similar ball of shit in NB. Patience is the key word, and never, ever tell them anything they don't ask for and for heavens sake DON'T tell them you bought it out of province unless you get papers from NS first!!!!
Now taking a step back, if they DO have a record of it, then they will try to contact the last registered owner on your behalf...good luck with that...