I've been working on some wheels for my featherweight which I have 3d printed and threaded with tap and die. Even though I've tested and they've worked as they should, I'm worried about the durability of these threads and I'm looking to redesign the wheel to a design more like this:

The question I have is does anyone know where to find these 3/8 (M10) 1-inch length brass hex nuts? I've searches everywhere for 3/8" Hex Female-Female Standoff, 3/8" Hex nut, M10 hex nut, etc and have not been able to find these. All I need is to find somewhere which sells this nut which is to be melted into the plastic.

Thanks, David.