Several available from Brownells, Badger is one that comes to mind since I have them on my rifles. Seems to be two styles, one that is a simple washer like the original but is about 2+ times thicker and a similar looking lug that is actually pinned in place. Held to the face of the receiver by pins that go thru it into the receiver face. There is a special jig to hold the first style in position as the barrel is screwed back on, not needed for the second style as it is pinned in place.
Believe that S1 makes and/or installs the latter style.
The aftermarket lugs are much thicker and stronger than the Remington factory lug.
ditto on the strength of the factory. the first thing my gunsmith does it hand me back the original and tells me to take it home,...he doesn't need it.
He makes his own lugs, with a extruded area on both sides of the rear, which fit into 2 recesses he cuts in the action face, that acts the same as the pins in the badger type. Much thicker, and much heavier in the hand when you compare them to one another.