The Polhemus plugin for Rhino is developed by Polyhemus, so the question should be directed to them.
Use the support page on Polhemus website.
https://polhemus.com/support/technical-support/
I do see the info indicates there is no download for a Rhino 6 or 7 compatible plugin and it indicates to contact Polhemus support if you are using a newer Rhino
https://ftp.polhemus1.com/pub/Software/Rhino/