Do you have a small light mic [not contact 'button type'] dynamic or cardioid, that could be attached via a 'goose neck' arrangement to my banjo?
The SM11 mic is often used on banjo. It can be attached to the tailpiece using Velcro.
Or consider the Beta 98H/C. It has a clip that will attached to the rims of many banjos, even though the clip was designed primarily for the bell of a horn.