UPDATE
We ship support for Xamarin.iOS and Xamarin.Android since version 2013R3. Customers with a valid support contract get the new platforms for free.
Are you not a customer yet? You can download Rebex SFTP as a free 30-day trial and start evaluating.
To buy Rebex SFTP, please visit our online shop.
These are not officially supported platforms yet, although we are considering adding support for them.
This said, Rebex SFTP is known to work fine on Mono on Linux, which means making it run in Monodroid (and possibly even MonoTouch) should not be too hard. One of our clients was even able to make Rebex IMAP work on his iPhone with MonoTouch with a bit of our help (we had to send him a custom build that links against MonoTouch's "System" DLLs, along with few workarounds), so creating a beta of Rebex SFTP that runs there as well might be a matter of several hours (with a bit of your cooperation). If you would like to give it a try, please contact us at support@rebex.net!