It is easy to make homemade isolators for an antenna.
Use any insulating plate of 1cm(or 1/2") thickness (plexiglass, ebonite or something like this). Cut the plate in bars.
Make a cave on every side of the bar as shown in the picture. Use for this emery wheel.
Cut every bar in pieces of 2cm (or 1") long.
Drill two holes under 90 degrees.
Dimensions are given in cm.
The isolator is ready.