VC:MP 0.4 supports custom objects, so you can try to port III's map to VC:MP.
It sounds like an insane idea, but it is actually possible.
You can fit in the limits of VC:MP by adding only the streets and buildings from III, then adding objects from original Vice City. Like palms, traffic lights, ramps, etc.
(maybe you can attach objects to another objects in some Model Editor, so you will be able to use more custom objects)
It will be hard, but the result will put a big and satisifed smile on your face.
PS: Use http://forum.vc-mp.org
next time, it's the newer forum, just about VC:MP 0.4 and newer versions.