I don't think its as rare as NWC.... Because NWC has a production number that we know of. 90 Grey Carts Exist and 26 are Gold.
Does anyone know how many copies were officially ran put into production of Stadium Events before they went "alright lets call it 'World Class Track Meet'"? Unless a number is released I bet there is alot more out there... Its just people don't know they have them. I am waiting for that day someone finds a long forgotten storage locker/container filled with these still in a box wrapped.