I'm delighted you have introduced me to this lovely looking route - Thanks!
As I implied earlier I'm in the lucky postion of owning a GPS device and have just downloaded the entire route to use on it
however, I like paper maps too and am sympathetic to your original question, so here's my tuppence-worth.
The french Michelin 1:150,000 do
have some cycle routes on 'em and you'd need only 2 (303 & 309) - they're a good price at Stanford's (buy 1, get the other half price!). All you need to do is check whether they've got the TdM on 'em - and even if they haven't, I'd buy 'em and spend an evening in front of the computer with a yellow highlighter.
My ony concern is that I'd worry that they don't have enought detail on - some of the minor roads in Normandy and Brittany are very
minor and almost certainly won't be marked on these maps. This has caught me out in the past, and I've tended to take maps with larger scales, IGN Top 100 is my fave) but I'm sure that all but the tiddleyest roads will be on the Michelins - you get used to spotting the ones that don't show on maps. Plus if you going to mark the maps up in the comfort of your own home you may well have the opportunity to spot any omissions...