winLAME is the external stand-alone version of LAME, which is usually inserted into Audacity in order to enable mp3 file conversion to Academy's requirements. Some people have trouble building LAME into Audacity. No sweat now, use winLAME (freeware): 

winLAME website http://winlame.sourceforge.net/

Just process through the wizard (Next >>) like this in order to get to the Bitrate setting box:

Input files > Output settings (click on LAME mp3 Encoder) > Presets (click on Custom settings) > LAME settings (Bitrate ...)

It is somewhat hidden, and not well described in the Help.

But the box for 64 bitrate is there...

James/Eurominuteman