Are you carrying it stand-alone? Or are you forced to have it mounted? Are you looking for a holster, grenade bandoleer, or pouch setup?
Our 1SG put out the SOP all our M320s would be mounted which had, IMO, some real downsides. However, before the SOP was pushed out I got an S&S M320 holster for T&E and one of my guys carried it that way for a few drills. He really liked it, could carry it under the arm even while wearing a ruck and could employ it quickly. It's also surprisingly inexpensive for the brand and product.
While at XCTC our company was chosen to T&E M320 holsters and, because of the SOP, they were all shoved in a bag and forgotten. I ended up getting a full MMI holster setup. It's work $4-500 and came with a single point sling, holster, and MOLLE belt. Overall it sucked. stitching sucked, it was bulky, and clunky. One of the guys ended up giving me his and I gave the MOLLE belt away to a coworker for his pistol, and later on sold the holster itself.
I have lent out both the S&S and MMI setups in the past so both companies would get additional T&E value out of them since they didn't respond to my emails to have it returned. I recently sold both to deploying soldiers who needed holsters (and I needed money).
The S&S is a the best option. It's inexpensive, adaptable, uncomplicated, and lightweight. The MMI is heavy, bulky, expensive, and complicated.
https://www.sandsprecision.com/weapon-retention/grenade-launcher-holster.html
ETA: Not a grenadier, I was a PL and XO trying to get my guys good stuff.