New Rims for 300 GES (5x130)

 Very limited choices. MB G-Wagen original alloys 15"  up to 19" (or more?) are the best option. Other options are Porsche Cayenne and VW Toureg (but not all, others can advise better). MB Sprinter steels. Also military Hutchinsons, also big money. Some UK specialists make adapters to allow other wheels to be fitted like Land/Range Rover but I have no contacts on that front.
Eddie.

You have to be a bit careful when looking for aftermarket wheels for the G because of the fairly rare PCD and centre bore dimensions.

You are correct that the PCD is 130x5 but what is just as important is that any new wheel has the correct centre bore which is 84.1mm.
The offset (ET) is also important because if it is greater than the standard 63mm then it risks fouling the steering arms, which sit very close to the wheel  on a 463.

By using the above figures you can work out that for a wheel to fit your G correctly it will require the following dimensions:-

PCD.                130mm x 5 studs
Centre Bore.    84.1mm
ET.                    63mm or less

I hope this is of some help with your search.