Replacement small parts

[ejtrent]

Basically, on my 416 ive managed to shred the threads on the plate on one side of the attachment that holds the front RIS on, see that block in the top right of the picture here..

http://www.phoenix-supplies.co.uk/me...k/hk416_05.jpg


Thats it. There is one each side, one has a thread the other doesnt, so I was wondering, currently ive got a nut on in place of it, it looks kind of rubbish, is there any way i can get a replacment? ive tried tapping new threads and it doesnt seem to work.