The getTribe arguments are appended to the api call as such:
&getTribe={name}
The possible arguments are:
ABRIN
ADUATUC
AEDUI
Ambiani
ARVERNI
ATEVLA
ATREBAT
Atrebates
BAIOBELLOVA
BITURIG
BOEOTIA
BOII
British
CALETI
Cantii
CARNUTE
CARTHAG
CASSAND
CAVARES
CENO
Corieltavi
CORIO
DAN
DIABL
Dobunni
DUROCAS
Durotriges
EBUROV
EBUSUS
ECCAIOS
ELUSATE
FAN
FOR
G-B XA
Gallo-Belgic
GER IND
GERMANU
GERMANV
GREEK
HAM
Iceni
KAPOST
KASTILO
LEUCI
LEXOVII
LIN
LINGONE
MASSILI
MELDI
MOU
NAM
NAMNETE
NERVII
Northern Italy
NULL
NUMIDIA
OSIS
OSISMII
PARISII
PHILIP
PHILIPP
PTOLEMY
RED
REGEN
Remi
RHONE
SENONES
SEQUANI
SICILY
SUESSIO
SYRACUS
Treveri
Trinovantes
TRUMPET
TURONES
UNCERTAIN
VELIO
VELIOCA
VEN
VENETI
VOL ARE
XN
Several of these tribes are due to be deprecated as clean up occurs. These will be removed from the documentation.