are you talking about this?:
Good luck. The rail kit for airsoft is a 1 piece floating sleeve and the rail on the top is not monolithic all the way back to the rear sight. The kit is also only made for AEGs, so to get it to fit to a WE, you need custom work. There was only ever 1 rear rail piece that mated up to the airsoft version of the rail, and laylax hasn't made it for years. I've tried to find one but no luck.
The real steel rail is a 2piece system, and probably would not fit an airsoft rifle, even for the WE, and you'd be looking at serious cash as the quadrail is an integral part of the m1a... someone would have had to bought one and changed it out along with the stock, and at that point, they could've started with another version that didn't cost as much.