Originally Posted by
Kettering Northants QC
Strand Travel in the UK used to do it but they've just retired.
Best to go with the line directly but choices are far fewer now (up to 1/3 fewer lines).
For those conversant in French, try
http://www.mer-et-voyages.info/. Nice online catalogue with pricing. They put on seminars in French if you happen to be in Paris.