You can get aluminum flashing at the hardware store ie: 6” X 25” X 0.014” for about 16 bucks.I don't think there is an actual name for them or a commercially sold product for that specific use. Usually you just make your own using shim or sheet stock. You can use copper or aluminum as well.
Most local hobby shops sell strips & sheets of brass & aluminum made by K&S that you can cut with sheet metal shears.
Hardware stores also sell strips of aluminum but I think 1/16" or 1/8" is the thinest they carry.