You can try the Mile High Table of Products here: http://www.deansdirectortutorials.com/MileHighTable/
Specifically, it looks like UltimateNet Xtra will work - but the Mile High Table lists it as D11 compatible, yet the website itself doesn't... I guess you will have to test it in D11.5: http://www.starsoftmultimedia.com/xtras/UltimateNet/
I'll take a look at the list.
I have UltimateNet Xtra but it only does FTPS which is FTP with SSL / TLS not SFTP which is SSH File Transfer Protocol (sometimes called Secure File Transfer Protocol or SFTP)