Go to the nearby store, explain what the problem is, and they will probably sell you an assortment of sizes. Then you can take them home, figure out what fits, take the others back, and buy enough of what you need.
They will have made a small sale and a lot of good will to have you spread around the community. My local hardware does stuff like that all the time, especially with plumbing bits and pieces. They even take back sections of PVC pipe after you cut off what you need. You can also buy it by the foot, obviously.