Well, I betook myself to the Wallace Collection today in the rain and, indeed, found a magnificent shiny fountain, adorned with muscular caryatids.
After a pleasant wander through the first-floor galleries (my goodness, that guy just didn't know where to stop with his collection of paintings!), I ducked into the shop and saw on the very first shelf the guidebook mentioned above. French-published, and in two languages, it contains suggested walks around Paris to find all the fountains. Looks great fun, though at £11.95 a copy I thought I wouldn't invest in it just yet. Better wait till a trip to Paris is in the offing.