I looked up if there was some trick to make a regex match a pattern but without repetition, if we simplify, then
(?:a[abc],)+
should not match "aa, aa,"` but will match if they are "aa, ab,". And of course I look it up, land on
Regex permutations without repetition which is at least promising but is
closed as a dupe. To a completely different question about using Java to find permutations of words.