Not sure what companies gauges you're looking at, but check to see if they list interchangeable gauges like PTG does:
View attachment 537596
... or just do what I do and put a few pieces of tape on the base of the go gauge to make it the right size for a no-go gauge.
Regarding your last statement, it would make no sense at all for a barrel manufacturer to stop offering a chambering just because some retailer can't keep everything in stock for someone to get fully set up to build and reload for a new rifle. Think of all the guys who are already set up and are working on shooting out their current 7 SAUM Proof barrels.