I haven't done any for so long that I have no idea where to go now so any help appreciated. This is for motorcycle parts (you guessed) exhausts etc, and companies doing this in small batches seem few and far between now compared with grit/sand blasting on an Industrial scale. I have used a place out Aldershot way in the past but some of the prices made it cheaper to buy a new (s/h) item in some cases by the time you've added paint.
i have used I cleenz machinez they are in tulse hill/west norwood south london they do soda blasting too very good service and reasonable price
I remembered a company in Hersham and just gave them a ring to find that their works have just been burnt down!