Can't give you an answer on that, but I was paid a visit in my Cornish bookshop about 12 years ago by a gentleman who'd written a history of the Hillmaster lorries and coaches, of which I admit to never having heard of, and think I bought a copy for resale. Just can't remember whether he said any were still extant, but I'm sure the book would tell you if there were. It appears to be listed on Amazon, though unavailable in practice.