Can't help with the parts but I can send you the Velcro.
I usually look to a sling that cartridges can be securely stuffed under a slack band, or one with a designated pocket sewn into them. I don't think you'll find a velcro set up for just two rounds. Velcro set ups usually will have enough cartridges to refresh the box magazine.
Quite a few companies making 2 round holders the attach to the side of your rifle with velcro.
The sling style are pretty much useless for competition shooters and aren't really that handy if you need a round in a hurry.
I usually look to a sling that cartridges can be securely stuffed under a slack band, or one with a designated pocket sewn into them. I don't think you'll find a velcro set up for just two rounds. Velcro set ups usually will have enough cartridges to refresh the box magazine.
Okay, but why are you bolded and in a weird font? Careful, some people might take it to mean you're yelling or being otherwise aggressive with them. But, I'm certain that doesn't apply to you, you're a gunner and therefore a nice guy. Perhaps you could assist the OP by hot linking 3 or 4 of those companies? I think the 3D printing could be an option so long as it can be mounted properly?
Also, I don't recall the OP stating the rounds were for competition. Perhaps I missed that?