Am after a 3" to 70mm exhaust reducer in stainless. Anyone know where to find one?

I think you willneed to get one from an exhaust specialist, maybe even get one made at those measurements.

http://www.tonylawexhausts.co.uk/2410/frames.php

is it to be weld on or slip on/in ?
I could possibly try and make one up

Dan, drop these guys a message on the Exhaust Reducer Connector Adapter - Made to Measure | eBay.

ATB Dan.

I used the eBay company above last week for a reducer, they made what I wanted, to the exact length, and it arrived the next day, great service, and great price too!

Cheers

Adrian