Now those are some cool and well proportioned mini choppers.
Re seats... you can make one and get it upholstered. Check The Chopper Shed posts for how to build a seat.
You can make a simple springer for your chopper too. Look up plans on the internet and scale them down. For your purposes, you wouldn't need fancy bushes just carefully drilled holes and close fitting bolts. they are not hard to build and you just need to be able to accurately cut steel to length and have a bench drill to drill the holes accurately. Once you have cut out all the parts, take them to a welding shop. You can go to a spring manufacturer to get some springs.
Sissy bars are easy to build. Get a long length of half inch round bar (solid steel rod), find the centre and bend it around a piece of 1"-3" pipe held in a vice. Then make two tabs with holes to weld on to the bottom of the sissy bar to mount it on the frame and another piece to run horizontally to support the fender and hold the sissy bar upright. Drill it and cut it to length and get it welded. There are a variety of fence castings that you can add to the sissy bar to make it look cool.
Well that's my bit for the moment, hope it gives you some ideas.