Any butcher shop/supermarket has beef marrow bones. They will cut smaller if too large for you. They used to be FREE! years ago because they'd throw away.Now they're for sale...usually $1.59-$1.99 lb?or so? Good luck with veal marrow bones*
Skagit River Ranch, which sells at the farmers' markets, carries them on some weeks. Just ask if they have them. They're delicious, and they're from grass-fed cows which means they're higher vitamin/omega-3 fatty acids than from a cow fed grain.
Bob's Meats in Columbia City has veal bones. Can't think of the price/lb. I remember thinking about the large quantity of bones that was called for in a Saveur recipe for demi glace and calculating that it was alot of $.