It’s not exactly easy for AR-15 builders to find everything they are looking for these days. However, if you are looking for a popular 10.3″ barrel with a Crane Spec .070″ gas port, Andro Corp has them in stock.
These barrels are a produced made Ballistic Advantage. They feature 4150 CMV steel with a Melonite finish throughout including the barrel extension with M4 feedramps. They have a 1 in 7″ twist rate and carbine length gas.
If you building a MK18, this may be just the ticket.