Recently found on Ebay, and bought for £21 is this NOS rear mudguard. This was a handy find, as my rear is not in good condition.
Old Stock Genuine BSA Tracker 125/175 rear mudguard in white. This will
also fit the NVT Rambler 125/175. I got the last two from the factory
in the 1990's"
The black line is a pen line (that will rub off) and apparantly shows where the guard needs to be cut on some models.
**** The same seller is now offering the other one referred to above. See here ****