Your model sounds like a Triang copy. Lots of these were made once the originals were no longer available. to be kind to the makers, they were probably home made for their personal collection (the theory was that you could probably claim this was for "reseach purposes" and unlikely to be a breach of copyright and in any case Triang only claimed "Patent Pending" on the casting) and were not attributed. Copies would probably date from 1980s onwards.