Hypnale, no, never seem them in the trade. I'm too young. That genus is from Sri Lanka and (as I recall) India, both of which I believe haven't exported live snakes for a very long time. Oh, there are probably some European-smuggled ones, or rather their progeny, out there but...no thanks. Actually, maybe there are some legal ones out of Tula or some such, now and then you see some neat critters out of there. (I live in Utah now, and getting permission to just keep native hots is turning into a multiple-year ordeal. So I've pulled my nose out of the exotics breeze; I don't really know what's going on. If I ever did.)
Ovophis is a genus that attracted me too, but...too spendy, and who knows about the consequences of a bite?
See the Gloyd and Conant "Agkistrodon complex" book for more info on a large fraction of the Asian crotalines. And of course, the newer Gumprecht et al "picture book" is a visual treat.
Anyway, unless you have a serious "collector" mentality (like with stamps or baseball cards), why go to all the hassle and health risk of working with Hypnale etc when their ecological analogues (and virtual aesthetic twins) are readily available in the form of Porthidium, Atropoides, etc, which as we have discussed are really under-appreciated anyway? And antivenom is also available in the event of an accident with them.
I kind of feel similar to when (for example) you're talking with a teenager who might not even have a driver's license, and they're going off about how much better it would be to have a Ferrari than a vintage Camaro (or whatever). And you think to yourself...only the trust-fund kids get to start with the Ferrari, and they often wind up dead or vegetables for their impertinence. And you want to say "Hey, why don't you start with the Camaro, if you're serious about this? It's a sweet car, still plenty fast, and you'll learn a whole lot about cars and yourself. Then if you still really really want to, after a while you can aim for the Ferrari."
Just trying to be helpful, and share some perspective.
Cheers,
Jimi