That is a Canadian serial (production) number from about 1977 (the records are a little sketchy).
It would have been built in Mississauga Ontario which was Merc Canada while it was in business.
Most online parts lists that you can access give US serial ranges. In this case you can use 4605112 which would be "mechanically identical".
Now trying to get parts from a Merc dealer for a motor of that vintage may be challenging at best.
For parts reference, this sites page for that model is here:
http://www.marineengine.com/parts/mercury-outboard-parts/110/3795658-thru-4839253-usa
A quick look shows more "no longer available" than anything else so you may have to go to a specialized dealer of more vintage parts. I live in Eastern Ontario and one of my "go to" parts source places is Laing's Outboards (they are in the Buffalo NY area). They will mail order up here no problem and they have a decent supply of vintage parts (I get parts from them for my own 1961 Gale (OMC) outboard).
So if you can't source what you need from the limited parts still available from Merc (or Sierra - an aftermarket seller), then Laing's may be able to help you out.