Are you looking for an adjustable "gas cylinder lock screw"? Brownell's sells SCHUSTER adjustable gas cylinder lock screw.
But honestly, you don't need an adjustable one. The normal one is just fine. If you need one, they seem difficult to find right now. Again, Brownell's sells the FULTON ARMORY one.
The idea that you need an adjustable one has been shown to be false. CMP (THE Garand experts) have said that standard 30-06 ammo is ok. If you are using hot loads or something, well then yes, you probably need an adjustable one, but you are probably also putting your entire rifle at risk. 70 year old guns shouldn't be used to fire loads hotter than the gun was originaly designed for.