If you do a quick google search for “small plastic plugs” there are a plethora of them.
Also, if you look under “Delrin plugs” you should find a bunch of plugs for people with gauged ear lobes. if you find the right size those would work perfectly.
Here is a link to something i found really quickly that would most likely be very suitable. just confirm with yourself the diameter of the hole and purchase the appropriate plug.
If you have any other questions let me know!