I have never seen NEW 7MM Gibbs brass for sale unless someone was getting rid of some of their fired stuff.
All Rocky Gibbs cartridges were based on the 30/06 case. You can make your own from the 30/06 or take the 270 or 280 brass, trim the overall length to 06 measurments (about .050" off) run the case in your 7mm Gibbs die to expand the neck from .277" to .284, fire form it and you have 7mm Gibbs brass. You can also use the 280 Remington brass, trim to the overall length of the 30/06, run it in your Gibbs die and fireform that one too. No expanding of the neck if you use the 280.
The Gibbs line was a fine group of cartridges. All had the 35 Degree shoulder and held about 9 more grains of powder over the standard when fireformed.
Grayback at one time did indeed sell sell the Gibbs in 7, 30 and .240...not sure if they still do.....my buddy some years ago purchased some in .240 and as I recall the shoulders were NOT fully firefomed and rounded. The brass also was very pricey. The brass was formed to the correct datum line . Of course you still had to fire once to get a perfect fireform with the 35.0 degree shoulder...hope this helps