Slim to none. Histrionicus are around but you need to have the right connections and experience. Mysteriosis not a chance. I do remember a post a while back about Inibico working on a project with Mysteriosis to have them of legal status in the US. Maybe in 5 years?. Hope that helps.
The man to ask would probably be ChrisK. I see a lot of his Histrionicus on site. I was reading some older posts today when Chris first got his Histrionicus and they were of legal paper work and ect. You might want to Pm him for better info.
Histos are around, and more recently I have been seeing more threads with pictures and breeding with them, so perhaps they are building in number more. Either way, most people with them either keep offspring for future breeding or trade with others for different rare obligates usually, so it's not very likely you will see a general "for sale" ad to anyone for a frog like that.
Mysteriosis are illegal in the US. I've heard people claim they are here, but "underground," though I don't personally know anyone with them. I have also heard some talk about INIBICO getting papers to bring them in legally, check out the thread that was in the last week or so in the General section about them. They are common in some European countries that allow them, but Peru claims to have never allowed them out and the US won't let them in for now.