[DPJ]

I was in Monte Carlo back in 2008 and 9 - I know, forever ago!!! But there was an amazing slot car and model shop across the street from the main marina. I can't imagine its still there, but you never know! They Love their racing cars!!! Ask a local and I'm sure they'll know of a spot.
I also lived in Barcelona for about 9 months - several great slot shops there, again... ask a local and they'll set you straight!