http://www.koha.org/support/ The first link takes you to a list of companies that provide dedicated Koha
services. "Pay for Support".
It's however an incomplete list. I say incomplete because over the years,
other commercial companies have done successful implementations of Koha but
might not have added themselves or might not have been added to this list.
Good business practice is to look for credentials and reference sites of
course. But as Paul Poulain says: most of the Koha distributors are not
limited by their physical geographical location.
http://wiki.koha.org/doku.php?id=kohausers The second link will take you to a listing of some of the users of Koha
around the world. Incomplete list most likely as some libraries don't know
of this list or choose not to be entered. However the listed libraries often
give their contact references. If you are looking for localised support
perhaps this is a good start.