Not to nitpick, but what is an MP4? Do you mean an H&K MP7? If so, I don't think that is one. I think it's a Steyr TMP.
Sorry, just giving you a hard time.
I've never seen a rig like that or anything close to that. (In real life, I doubt anyone would ever wear or need something like that) I'm guessing it is a complete custom job. Some straps from leg rigs look like the only found part. The frames that hold the TMPs look like they would have to be custom molded or machined. It may use either magnets or perhaps locking mechanisms from race gun holsters to hold the TMPs in place.
Yes from my inquiries with the weapons guy its all custom pieces with the leg straps used from military gear....im still searching for the holster pieces.