Complete the following in Co-Op mode to unlock the guitars. This does not include "Extra" songs.

Code - Effect

Cream SG - Get 5 stars on 20 Co-Op songs
Gibson Grabber - Beat 20 Co-Op songs
Gibson SG Bass - Beat 10 Co-Op songs
Gibson Thunderbird - Beat 30 Co-Op songs
Hofner Bass - Beat all Co-Op songs
Lava Pearl Musicman Stingray - Get 5 stars on 10 Co-Op songs
Natural Maple Gibson Grabber Bass - Get 4 stars on all Co-Op songs
Natural Sunburst Gibson Thunderbird Bass - Get 5 stars on all Co-Op Songs