CW, it's about impossible to find a good price on a 124. I had one and sold it years ago, and I'm still kicking myself for it. I keep checking the big auction site, but it's not going to happen, not at a price point I am willing to pay, anyway. For what they are selling for, unless it was the last piece I needed to finish a collection off, I'd spend it on a custom.
The only diver's knife I know about is the 185, which is a version of the 184 Buckmaster, but instead of the hollow handle, it's a full tang handle with a coating on it. They're going for big $$ too.
Honestly, Buck's 420HC is a good value. It's not a premier steel, but it's still heat treated by Bos to an average hardness of 59RC, which makes it perform much better than you think it would. Most other companies run their 420HC in the 55-57RC range, and you can definitely tell the difference.