depends... there are sightseeing orient express journeys... you can even do them in the UK... or you can go on the route on the standard trains.
i used to go through deutsche-bahn (sp) a UK based euro-rail firm, they are based in surbiton. for french train trips you can book with sncf direct and they'll send the tickets to the uk.
you can probably do it through last minute and the like now, i haven't done a euro rail trip for a while. i know swedish rail trips are a pain to book, but the orient express route should be easy.