On some forum, in the past, I saw a post that indicated a gunsmithing outfit in the UK had made extended magazines for the .223 BLR, which is itself a rare bird. I went to that outfit's website, and did not see that listed as one of their services, but of course just because something is not listed does not mean a talented 'smith could not do it. I apologize, though, as I cannot recall the name of the business, nor the forum on which I saw the post.