What comes after twice and thrice?

Answer 1

Once, Twice, Thrice, Quarce, Quince, Sence, Septence, Octence, Novence, Tonce, Elevonce, Twolce, Thorce, Quartonce, Quintonce, Sextonce, Septonce, Octonce, and Noventonce...

Unfortunately, it stops at 19 times.

Answer 2

It is nothing that comes after once, twice, thrice.

However, some people did create some protologisms for the "-ce" series:

1. Some people use "frice" after "thrice", which has been attested by Google Books Ngram Viewer.
2. The "-ce" protologisms by the DROD computer games: quarce, quince, sence, septence, octence, novence, tonce, elevonce, twolce, thorce, quartonce, quintonce, sextonce, septonce, octonce, noventonce.
3. Pure Latin protologisms of the "-ce" series: quarce, quince, sence, septence, octence, novence, decence, undecence, duodecence, tredecence, quattuordecence, quindecence, sedecence, septendecence, octodecence, novemdecence, vicence.
4. Pure English protologisms of the "-ce" series, which are compliant to the etymology of "once", "twice", and "thrice": fource, fifce, sixce, sevence, eightce, ninece, tence, elevence, twelfce, thirteence, fourteence, fifteence, sixteence, seventeence, eighteence, nineteence, twentice.

If you really need such things, choose the one you need.