Is it possible to have a Supreme Awning made with 6' width? I have a custom built camper.

Yes, It is theoretically possible but there are compromises required. The front bar length of an Supreme 8' awning is 92 inches. The projection of the standard Supreme Awning is 84 inches. For every inch less than 92 inches of front bar, you lose 1 inch of projection.
A 6' Supreme Awning (with a 68 inch front bar length) has a projection of 60 inches (5 feet).