Dis you download this one
HERE
There is one here also called Bongos TBC but it is oudated.
And just to verify you said the folder structure is right.
Should read :
C:\program files\WoW\interface\Addons\Bongos\
C:\program files\WoW\interface\Addons\Bongos_ActionBar\
C:\program files\WoW\interface\Addons\Bongos_CastBar\
C:\program files\WoW\interface\Addons\Bongos_MapMod\
C:\program files\WoW\interface\Addons\Bongos_Options\
C:\program files\WoW\interface\Addons\Bongos_Rollabr\
C:\program files\WoW\interface\Addons\Bongos_Stats\
C:\program files\WoW\interface\Addons\Bongos_XP\
Also those Blizzard Folders stay. There what blizz uses for their basic UI stuff.
I know you said this but just wanted to make sure it is absolutely right as the number 1 reason for no addon button in the char select screen is people tend to either place the files out of their folder structure (files only) or in the case of addons like Bongo, which have multiple folders, they place everything in a folder labeled Bongos.
Hopefully this will help you. If not try another addon and see if that works.