There are various epigraphical references of Numidius as a nomen:
CIL VIII 23074 (Ain Batria): Aurelius Numidius P[3]nsi[3]
CIL X 3824 (Capua): Cn(aeum) Numidium / Astragalum
CIL XIV 3627 (Tivoli): C(aius) Numidius Qua/dratus
ILCV 297 (Santa Maria Capua Vetere): Murrius / Numidius
PanDeser 64 (Berenice): C(aius) Numidius Eros
In CIL VIII 5301 (Calama) is used as a praenomen (Numidius Marius), while ILAlg I 2071 (Madauros) records it as a cognomen of Q(uintus) Domitius Numidius.
The most famous person to which has been attributed the cognomen Numidicus was Q. Metellus Numidicus (cfr. e.g. Cic. Brut. 135; Vell. 2,9,1; Val. Max. 3,8,4; Gell. 15,14,1), who fought against Jugurtha in Numidia from 109 a.C. (see also CIL VI 40942 [Rome] Q(uintus) Caec[ilius L(uci) f(ilius) Metellus] / [Numidicus]).
Other epigraphical references of that cognomen are:
CIL VIII 15667 (Kaussat): P(ublius) Larci/us Numidicus
CIL VIII 16104 (El Kef): T(itus) Largius / Numidicus
CIL VIII 25660 (Chemtou): L(ucius) Iulius / Numidicus
IScM V 00270 (Isaccea): Mar]cianu[s] / [3] Cassius Numidicus
RMD IV 223 (?): Ti(berius) Claudius Numidicus