Sliding Licence Plate nuts

[Bluechrome]

Hi

I have lost one of the sliding nuts that hold the licence plate on. There are two of them and they fit on the rear fender while the licence plate bolt threads into them.

Any one have a part number or alternative way of attaching the plate? I can't find it in the parts listing for any of the models.

My bike is a 1987 Venture.

Thanks in advance.