I have a 459 that I bought new in 1986. I have never carried it in a holster so I can't offer any specific suggestions. However, becasue the gun silhouette mimicks the 1911 I would find a cooperative gun store and ask to bring the 59 in to match up against a current 1911. Once you find a close match, use the 1911 in your search.
I am extremely fond of my 459. I have recently toyed with a desire to try a grip that has an integral rest for my thumb. I am thinking this might help my accuracy just a tad more. Just a thought. Bad news, no such grip exists, at least as far as I have found. Also, true factory mags are very hard to find and expensive.
If you decide you don't like it, PM me.