Original exhaust wud hard to find. as a work around u can get them fabricate localy.
Original Carbs of GSX 750 shud be easily avaialble they shud fit & work perfectly with out any modification.
Tail insatalled on Yellow bike in pics looks same as of GS 550 which can be found (one i have wid me)
Complete seat can also be fabricated localy instead of searching Genuine which is hard to find.
Can u post some pics & deatils of ur project so we can comment better ?