We were fortunate to be able to visit the Alex Singer shop in Paris when we were there for Paris-Brest-Paris in 2011. Even got to check out the back of the shop, which was overflowing with stacks of parts and an amazing assortment of Singer and other bicycles.
For those who can't make it to Paris, here's an interesting video from French TV. It's only in French (no subtitles), but you can learn a lot just from watching.
Update! Couple of photos from my visit to Alex Singer: