Correct. Sean Stewart did bring some in many years ago.Not too recent but around 5 years ago Sean Stewart had some on his website from a shipment from Europe.
To the OP, you don't see them anymore because they are from Peru which has been closed to WC export for some time. Last I heard, understory wasn't able to get permits for macero, although I believe they're working with cainarachi. Very similar looking frogs.
Also correct is UE. They are currently attempting a breeding program with them, but it is still in the infancy stages.
Same with Silverstonei.
Whether it will be successful or not remains to be seen, but if it is, it will probably still be a few years before they will be formally introduced into the US hobby.