Okay-- I've just looked at the MCL website and the authorized uniforms available through their "ship's stores".

1) Red mess dress jacket: This is fine for kilt wear.
2) Gold, four button vest: This should also work for kilt wear.
3) Black dress shoes: Works fine with the kilt.

So, unless you want to ask HQ for permission for a different uniform for wear with the kilt, it looks to me as if 90% of everything you'd need/want for a kilted uniform is already authorized. In other words, all you need to have authorized is the Leatherneck or USMC traditional tartan kilt, a plain black leather sporran, the blue hose, and red flashes. Everything else is there, and off the shelf at Ship's Stores.

It's just a hunch, but I think you have a better chance of getting the kilt/sporran/hose/flashes authorized, rather than designing a whole new uniform for kilted MCL members, and trying to get that approved by HQ.

Either way, good luck Marine!