I have two used Roland GK-3B pickups for sale. One came on a Roscoe bass I bought on T/B, the other, I don't remember - looks like it's never been installed. (see pic's)
$110.00/each shipped CONUS
note: this sale is for the pickup only, I don't have any mounting hardware /screws.
Often these units are mounted using two-sided tape to avoid drilling holes.