last year Manx Post Office's Xmas book had a section devoted to the P50 and other cars (+ all the stamps showing the cars - I gave a framed minisheet of P50 stamps as a present), there may be some of these still available but they usually sell out as effectively the book is free with the included £30 of stamps - I think the Transport Museum in Peel which owns a P50 and is some 100 yards across the Neb from the design office issues a small fact sheet + brochure