I emailed the guy at Westcoastime.com a couple of months ago about his inventory and he replied that he was expecting them back in stock in a few months. So, I think maybe May. In the meantime, I just took an older strap I had and used a hot finishing nail to put holes in it all the way up the strap. I use that second strap as an extender.
I mostly dive dry, but I still used my Zulu strap with a wetsuit while down in Bonaire (so only a 3 mm). I just cinched it down nice and tight and it was fine at depth. Not sure how it would work with a thicker wetsuit suit though, since I have no experience there.
One tip for 5-ring Zulu straps that a lot of people skip: weave the strap belt-buckle style through the rings at the bottom. This way, when you cinch the strap down tightly, you don't put stress on the bottom pin. Instead, the tension goes to the bottom rings.