Hey, it's been a while since I've been on the forum, but I thought I'd try to help a fellow free stater out.
I've never had one, but every once in a great while an Orthosternarchus tamandua pops up for sale on aquabid or here on the sales forum. I've seen them everywhere from $60-300, and haven't heard too many success stories on shipping or keeping one long-term (pretty sensitive, deeper water knife).
If you really have to have one, your best option would be to get in touch with one of the exporters out of Iquitos or elsewhere in Peru, and have them catch one/a few for you and ship them into their US distributor (some may have a US branch to handle importing so you can get them shipped directly into MCI from florida or wherever without transit time extending too long).
Just a couple of exporters I pulled up on google:
http://www.aquatechnics.net/
http://www.oafa-aquarium.com/
http://aquarium-panduro.com/macro.htm
I've done airport to airport shipping before, but I've never have anything imported specifically for me, but I was looking into it to get some compsaraia. Let me know if you are interested in taking the plunge on this, as I might be interested in splitting the shipping costs, depending on whether the price is right or not.
Hope this helps!