inquam and aio are defective verbs and you can find their complete conjugations in A&G §206.
inquam appears to be a 3rd conjugation -io verb, though many forms are missing from its paradigm and the 1st pers. sing. pres. act. indic. is thought to be a subjunctive form in origin. The common forms of inquam are:
inquam "I say"
inquis "you say"
inquit "he/she says"
inquiunt "they say".
inquit is the form you will no doubt encounter most often. This verb often seems to be used with a past sense, though you could just consider it historic present.
aio is just another 3rd conjugation -io verb with some missing forms. The common forms of aio are:
aio "I say"
ais "you say"
ait "he/she says"
aiunt "they say"
It is regular in the imperfect, as aiebam, aiebas, aiebat, etc, but you will most often see it in the present.
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae