Master cylinder cap? That's easy, buy a set for a VS800 Intruder and sell the spare one. It is the exact same master cylinder, just has an extra lid for the hydraulic clutch, which uses the same top plate.
Mirrors: any HD with the 10mm adaptor kit. Or Honda or Kawasaki with 10mm stem threads.
Grips: any HD
Lights, signal: aftermarket HD, I love the Custom Chrome units.
Pegs: VS except 1400.
Footboards: VS 800
Light, head: HD or VS800
Light, tail: happy hunting, nothing else fits without some tinkering.
Windshields: too many choices to list, including cafe racer 1/4 fairings and full fairings.
Seats: good luck, OEM or sprung solo.
Handlebars: any 1 inch diameter.
Exhaust: aftermarket HD fit fine, so do OEM HD.
Just a quick off the top of my head listing. Believe me, you can make most anything fit if you have a Dremel tool.

Check the Member's rides map photos.
-WD