Yay, I too am now a proud owner of a blue radius (and a mini...to add to my P3) came in the mail yesterday. vaping on it now with a kayfun.
Planning on losing that mini USB cover pretty soon. So, I bought 25 replacements on ebay from a US seller, for $6.45 shipped.
Uxcell brand seems to be the correct shape, I'll post again when they arrive.
Uxcell 25 Pcs Anti Dust Black Soft Plastic Dock Cover
I think the Uxcell mini usb insert is a realllly close match, same shape, and feel to the rubbery latex "plastic".
...but they're made in China, so...
An acceptable replacement for when I loose my original Radius insert. ..and one less request for Radius repairman Bill.