I’ve been farming Amach in Cursehaven on M10 and he’s dropping the Old God shield at a very good rate. I’ve gotten 3 of them in about 15 kills. Really surprising. I even got one with the ASE 50% elementary damage anoint, which has been very rare on the Xbox.
If you’re looking for an Old God shield, give Amach a try. He’s a lot easier to get to than the Empowered Grawn.