Here is the link for the speedometer but you used to be able to buy the whole thing http://whizzermotorbike.catalog.com/...group_id=48804
now you have to do it in parts so it may or may not be worth it, but it is a functional mechanical speedo.
Bar end mirrors are generally better because then nothing is blocking your sight (like your body) but if you want to go more for aesthetics then do whatcha want.
So long as the fork is beefed up you should be just fine, and I had no idea you were using a model A light and some kind of existing system. That sounds pretty darn cool man. I'd like to see a link for this light system now if there is one because I'm curious.
Yeah imperial cycles was the first place that came to mind but their site has been shut down (prolly because they were taking money) Ebay and swap meets are your best friends depending on what your time frame is. And if you have a minibike tank use it, and if the sportster tank looks good, use that. This is your build. I'm just offering suggestions but there is NOTHING more important than loving your bike because it's an extension of who you are.
As for throttles, all of the throttles can be made to work if you're creative enough, the napa throttle just has a classic look that the modern billet ones don't have. http://www.napaonline.com/Catalog/Ca...921_0238939007
ugly uncomfortable grips, but you can put something different on that twist tube than what it comes with.
Hope this has been helpful and please be sure to ask more questions. We're all here to try and help you not make as many mistakes as we've all made lol.