I don't own Dietrich's armour Nick, where did you find that info from out of interest?
In terms of where all the sets are now, not all collectors are as forthcoming as others in letting people know what they have. It's common knowledge (i.e. on his website) that a set of Apone and Crowe armour are owned by Aliensarchive. I believe a set of Apone armour is in the Propstore private collection and I've seen a Frost set too which they used to own. I have seen a few other sets including a Hicks but unfortunately I'm sworn to secrecy as to who owns it I'm afraid.
One interesting bit of info is that I was speaking to an Aliens crew member a while back and he told me that while he was working on the production he saw a skip containing several props etc. that had been thrown away; including at least one set of armour. He managed to salvage a helmet from the skip - of course in hindsight he wished he'd taken the lot!
Harry