I'm sure HK has a blueprint. They sell them, along with the tech package, to their manufacturing license purchasers. Anybody else, lotsa luck! Same with the FAL, everybody who purchased one of those raw castings from Tapco would kill for a factory blueprint. FN and DSA ain't sharing.
If you want a dimension I suggest using your gripframe as a template, mark the opening, then measure off the dimensions yourself.
The factory paddle parts can be made to fit any clone, the problem is some use a solid mounting shelf where the paddle goes. If the shelf is a "U" shaped piece that fits over the sheetmetal and is welded on, all you need to do is drill the blind hole and make the slot for the paddle. Some fitting may be required, but that is pretty minor. If the shelf is a solid bar of steel that was welded into a cutout in the sheetmetal, you have some work ahead of you. The inside of the solid steel shelf has to be hollowed out to accept the parts. Easiest way is to cut it off, mill it out, then weld back on.