Local shipchandlers should have all you need. Prefer the establishment frequented by anglers or professional inshore fishermen. Unless you are going to do an inordinate amount of rowing then its not worth spending a fortune.
My oars came with a cheap looking plastic collar. I didn’t fit them. Instead I went rowing -t o see where oars wear. Then I used some braided nylon line to do a whipping, then tied a Turks head in the same line (source- local hardware) All thi string was then treated to a good soaking in epoxy (made thin to soak in).Works well, might need to be re-epoxied one day.
The rowlocks are permanently attached to the oar – get some 2mm line, drill a small hole in the end of each arm of the rowlock. Line is treaded through holes and a stop knot tied at each end so that line is slack enough not to interfere with rowing but will not slip over collar or blade.
Buy a 3rd socket for the stern and spend the time it takes (about half an hour) to learn to scull