It really depends upon the date the trailers were built. The really dangerous crocidolite and amosite containing brake shoes have been banned from the early 1980s. However for trailers built before December 2003 there is a chance that the shoes contain chrysotile (white asbestos) and Defence Materiel Organisation therefore assumes that any vehicle with a build date prior to December 2003 contains asbestos, irrespective of the fact that they contain asbestos or not. Its called chain of responsibility and adverse risk avoidance.
Someone with the RPS should be able to give you the brake manufacturer part number or just contact track Trailers (Track Trailer) who made them in the first place.

