My brother is a stonemason, and at the moment a very good trade to be in, loads or work, not enough stonemasons.
He really enjoys it and currently works alongside another couple of stonemasons and has done for 2 years, he is now going to college on a day release basis to glasgow metropolitian college.
That page includes this quote:
"There may be the option to undertake a Construction Industry Training Board (CITB) Intermediate/Advanced Construction Award (Stonemasonry) at a further education college. Check with CITB-ConstructionSkills and local colleges for details."
From that, I assume that CITB should know which colleges offer the course. The contact details for CITB are on the same page.