I cite some of these sources by abbreviations, shown below.
CISP: Celtic Inscribed Stones
Project. A collection of work by many authors.
DIL: Royal Irish Academy, Dictionary of the Irish Language: based mainly on Old and Middle Irish materials (Dublin : Royal Irish Academy, 1983).
Lambert, Pierre-Yves, La Langue Gauloise (Paris, Editions Errance, 1995).
Evans, D. Ellis, Gaulish Personal Names: a Study of some Continental Celtic Formations (Oxford: Clarendon Press, 1967).
Macalister, R.A.S, Corpus Inscriptionum Insularum Celticarum Dublin: Four Courts Press, 1996).
MacBain, Alexander, Etymological Dictionary of Scottish-Gaelic (Hippocrene, 1998). Apparently a photo-reproduction of the 2nd edition of his Etymological Dictionary of the Gaelic Language.
McManus, Damian, A Guide to Ogam (Maynooth: An Sagart, 1991).
Schmidt, Karl Horst, Die Komposition in gallischen Personennamen in Zeitschrift für celtische Philologie, 1957, 26:33-301.
Thurneysen, Rudolf, A Grammar of Old Irish, trans. by D.A. Binchy & Osborn Bergin (Dublin: The Dublin Institute for Advanced Studies, 1975).
Layout, editting, and publishing Arval Benicoeur.