I know the Hillman parts boxes in hardware stores carry nylon (white plastic) fasteners.

Bolts, nuts, washers, and bushings (standoffs).
They come in a variety of sizes and lengths as well.
Some electric supply stores may carry that stuff for mounting electrical insulation boards.

Should be available online as well.

Barry, do you have a close up bushing

50vert wrote:

Dan's idea of a nylon bolt of the correct diameter is a good one.

As long as the nylon shears at the correct force.

Maybe some cheap chicom nylon

There are grades of Nylon.  I don't think I'd trust this to offshore made stuff of unknown grading. 

If those parts were part of an assembly I'd bet money they were never available separately.  If worn out your best option is good used.  If serviceable just use what you've got.  If neither options works you could probably have new ones made.  There are plenty of machine shops that work with Nylon.  You may even be able to have them 3D printed.  I know there is Nylon filament for 3D printers.  BUT, I would consult with someone with the engineering expertise to verify that the new parts are going to work like the old. 

Oh that makes more sense now thanks