This page provides information about the former NEC/Permeo socks5 reference implementation.
Permeo was a subsidiary organisation from NEC and was later part of Blue Coat Systems. It seems the reference implementation is not supported any more by Blue Coat Systems. No reference to it can be found.
Open Letter to Permeo: Response to Permeo not willing to release the source to an educational entity (Vienna University of Technology) showing their real intentions and unability to act as a real maintainer for the reference implementation, denying any coorporation regarding improvments, bugfixes and so on!