I have a couple of these that I've used on the standard A2 handguards, and made them work on the magpul handguards by using a roungd file to open up a little more space for the stud to fit through the M-LOK slot. They work fine.

https://www.midwayusa.com/product/404111/harris-bipod-adapter-stud-swivel-5-ar-15-black


Here's a pic of that mount on a MagPul guard. It works fine for a sling attachment or Harris bipod.

[Linked Image]