That's great. You can get metal-grinding round bits or round files, round sanding-bits, etc for $10 or less usually. Most people have a drill already or can borrow one.
Originally Posted by Gator Wrestler
I have developed a method of enlarging the sprocket hole that is quick and accurate.
I use a power hand drill with a round file chucked into it. The sprocket hole is placed over the round file and using the other hand to hold another file (I use a curved one) the drill is run at a high speed. The sprocket is allowed to spin and the action of both files on opposing sides of the hole quickly enlarge the hole. Don't forget your safety glasses.