This is the LAST place you want to be coming in telling developers what YOU want... not being rude but it's a developer forum.. you come here to learn to develop stuff for FS not request things as if they are super duper simple to do.
Yeah if you are paying them a full, fair wage through the years it will take - you will be paying them thousands.
If not, just wait until someone else decides it's time for them to model a G3.. the LAST thing you want to be doing is coming here with no experience what so ever almost demanding someone to make you an aircraft.. not only that but for FS2004.
In my opinion it's extremely unrealistic and nobody will take the time, no matter what amount of money you offer, to model an aircraft for FS9!
Also, if this is for a Gulfstream, note that they are 'very very' protected under copyrights. Even the shape of their side windows. If you 'think' about doing a payware of their plane for a sim, their lawyers contact you and try to shut you down.