After some searching around, it looks like the show is apparently using a Tex-Shoemaker holster after all. It's model #42-A. Rick Grimes is wearing it on a Sam Browne belt.

Here's the link if anyone is interested:
Walking Dead Holster at Tex Shoemaker and Sons Inc

Attached Images

Rick-Grimes.jpg (64.6 KB, 606 views)

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Ephesians 6 (Armor of God)