Home depot for sure, and maybe canadian tire or home hardware depending on your local store, will have 1/4 inch brass rods in 3 or 4 ft lengths for 10-15 bucks. You can't go wrong with that. It won't mar your rifling, it won't splinter/break and get stuck EVER, so why bugger around with finding a special piece of hardwood dowel that's going to cost you the same money and MIGHT still cause you problems?
Buy 2, so you can cut one into a 4 inch, 8 inch, 1 foot, and 2 foot sections. It's a lot easier to start pounding a bullet out (or pounding a slug in) with only an inch or two of the rod sticking out of the barrel so it doesn't bend.