The case head dimensions for the 6.5mm Grendel cartridge are close enough to those of the 7.62x45mm Czech that their stripper clips work. 7.62x39 clips won't because they're curved to follow the tapered case body.
One or two eBay sellers had the stripper clips. They're 5-rounders. For a 25-round magazine (C-Products in this photo), 5 clips fill it.
The GG&G stripper clip guides for 5.56mm ammo can be modified to take the Czech stripper clips. Bend outward slightly the rails that attach the guide to the magazine, bend outward a bit more the rails that hold the stripper clip to the guide. Your mags will get a little scratched.
The Czech clips have bumps that stop the clips from entering more than about .500" into the guide. The first clip will strip into the mag OK but not following clips, because there's too much gap between the end of the clip and the top of the magazine. The cartridges pile up instead of schmoozing on into the mag.
Your Dremel, with a cutting wheel, can carve open a slot on each side of the guide to let those bumps in so the clip seats deeply into the guide. The slots need to be long enough so there is barely enough space for one cartridge case head between the top of the mag and the end of the clip. The bottom round of the clip should be almost touching the follower.
The slots will be the width of about two thicknesses of cutting wheel, to accommodate the bumps. See the red markup on the photo. A needle file down the insides of the clip guide rails will help the clips to slide in squarely.
Wirebrush the slots to clean up your work. If you're obsessive, degrease the guide(s) and reparkerize or zotch them with teflon/moly.
I think a rub or two of paraffin on the clips themselves will help the cartridges slip out of them.