classic motorcycle forum

Hi I fancy getting hold of an NVT moped, not sure of correct model name, but the one with the tank and seat unit added to make it look more like a motorbike rather than a step through moped.
Can the step through ones (they seem easier to find) be modified by adding the tank/ seat unit along with the extra frame cover?
Do these parts come up for sale?
Any help or advice would be of great help.
Best wishes
Rob