David Novo
Contributor
Y-valve?
I don't think I've ever seen one of those in the wild. Perhaps because twinsets - both small rec twinsets like D8.5x232 and large technical twinsets like D12x232 - are really common around here. If you want two posts, just get a twinset.
I have seen Y-Valve tanks often in dive centers here in Portugal. If you want to dive a twin set, you usually need to own it.