I need to raise the crown race on a set of RS Rebas by about 2mm to prevent the gate adjuster touching down tube on full lock. Is it possible to buy thicker crown races and if so where?

Cane Creek and On-One both make headsets that give more Fork/Frame clearance.
http://www.chainreactioncycles.com/Models.aspx?ModelID=11258
http://www.on-one-shop.co.uk/acatalog/On-One_headsets.html

Don’t think anyone has fixed your problem that way, wouldn’t be kind to the steerer or headtube. the usual method is to use a headset with deliberately larger stack height. If a different standard model doesn’t do the trick, CAne Creek S-3 plus Five adds an extra 5mm, as doe the On-One Smoothie Regular +5mm.

Grrr, too slow, now I’m grumpy, Dave.

Doh! Should have thought of that myself- spent time on sites looking for first solution missed the obvious one.I’ll get my coat
Thanks Guys

You don’t necessarily need a +5mm headset. I had a Cane Creek headset and the adjuster fouled the downtube by about 2mm, looked up the specs of the headsets and realised that a standard FSA Orbit XL II would give me enough clearance without raising the front more than necessary 🙂