Sprocket suppliers + cat removal

[couchcommando]

Just about to take delivery of my own GS800 after riding the gf's one for a couple of weeks. Off road I prefer shorter gearing so where can I buy a 15t front sprocket and a 43t rear from ?
Also has anyone removed the cat and got a before and after dyno reading, was worthwhile on previous bikes so just wondering how the little GS responds to this ?

Thanks