Thanks a ton sir.I bought a 15 standard two years ago and also added the passenger backrest, rack, and center stand.
The center stand you can buy from the dealer or even eBay, but your best bet is a trike conversion shop. The trikes don't use them, so you can get them cheap.
I have one local that I asked...I gave $20 for the whole shebang.
The backrest and rack you have several options here as well. I bought mine all used takeoff from a forum classified.
eBay also has both. I've heard that some of the parts are no longer available from Honda, but it's hard to say what dealer stock is...so eBay is probably your best bet
I just went through the same thing. Thought I found 1 in Ohio but there inventory was wrong. Had to buy it from a gentleman on ebay. Shipping is kind of high but it coming from overseas. Maher him an offer he came down $25 on the price for me. Good luck