When a custom map has a side such as droid commando or swap speeder do the map makers make it do each map maker make their own or do they get it from the same source

What?

lets say for example a map comes out that has a side of a commando droid, is there a way to use that side

I'm pretty sure you are looking for this: viewtopic.php?f=64&t=12991

and no the units needn't to be equal. every moder can change everything on the side