It seems that mp3 to abc conversion is mostly related to a process of making musical notations (.abc) from some MP3 audio file. This should be possible with Harmony Assistant or any similar music notation tool that has this capability.
Convert Compressed audio and music file, mp3 songs or ringtones to Musical notation language file.
We found one software available in the database for this conversion.
Multiplatform software - convert mp3 to abc on any platform
A music composition and editing program
Convert from mp3 file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.