Not exactly local to Bath / Bristol but I had the (whole) elevating roof resprayed by this shop in Winchester:
centralparkbodyshop.co.uk
Reasonable price, good work and quick turnaround. Based on a recommendation from the garage that services my Cali.
Heritage (Westbury I think?) did the original repair to the front spoiler section back in 2014. This was when they were one of the 4 or 5 VW approved shops to remove and replace the spoiler (i.e
not put the plastic cap over the issue). That part of the repair is still good 12 years later. The elevating roof 'edge only' repaint they also did I had issues with (paint faded) , got redone by some place in Twickenham who took 6 weeks to do a very poor job that lasted a year. At that point I gave up on VW and had it done locally by central park.
While searching for a bodyshop ask early on if their paint booth can handle the height of a California, not all can and still be able to use the spraygun.