I was looking for a 737 with FMC functionality too, with no luck. However,
www.phoenix-simulation.co.uk have recently released what I am told is the most realistic Flightsim Pro2k add on, 747-400 with supposedly fully functioning FMC. I say supposedly as I have no experience of the real thing, but as far as I'm concerned it's superb and well worth the money! Maybe someone else can verify authenticity, apparently it was signed off by seving 744 flight crews....