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.
tated: "New 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.