Atticus,
Good of you to ask; that's how I learned about many of the accessories on my bike. The horn cover came from J&P Cycles...I think they run about $20 (but its been awhile...and my memory's failing). I added an HD medallion that anyone can pick up at their dealer for about $15. Here's a better picture of it:
I don't have a better picture of the axle covers. They're called 'Speedball Front Axle Caps' and are made and carried by Cycle Visions. I copied a picture of them from their catalog. When I bought them, I went through M&M Cycles, and at that time I paid around $65 +/-. A year or so ago I noticed that they had gone up in price considerably (I'm thinking about $120). They are a hefty piece of work and very well made. IMO, they're probably the best axle caps you'll see and they look really good on a RK Classic.
www.cyclevisions.com