That's interesting - since basically every auxiliary verb I can think of for english
(Am, is, are, was, were, will, have, has, had, may, might, can, could, shall, should, must, ought to, would)
has a contraction form with "not" (although some are fairly colloquial, or considered out of date):
(amn't, isn't, aren't, wasn't, weren't, willn't, haven't, hasn't, hadn't, mayn't, can't, couldn't, shalln't, shouldn't, mustn't, oughtn't to, wouldn't)
(Am, is, are, was, were, will, have, has, had, may, might, can, could, shall, should, must, ought to, would)
has a contraction form with "not" (although some are fairly colloquial, or considered out of date):
(amn't, isn't, aren't, wasn't, weren't, willn't, haven't, hasn't, hadn't, mayn't, can't, couldn't, shalln't, shouldn't, mustn't, oughtn't to, wouldn't)