Fulton has the 7.62 GO gage, and a few of the other MilSurp dealers might also have one.
All you really need is a .308 GO gauge, and cut out a recess at the back for the ejector.
The .308 GO is the smallest, and you can pad it out with shims cut from feeler gauges to get any bigger dimension you want.
Trying to make a gage SMALLER is a LOT harder than trying to make it bigger, by stacking up a few shims.
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