According to Wiktionary, the past participle of "flaw" is flawed, and flawn is not mentioned as being a valid alternative. However, the past participle of "draw" is drawn. I know that Modern English is irregular with regard to many forms and conjugations (for better or worse), but at first glance it is logical that the past participle form should be flawn, and not flawed. In short, what is the correct conjugation of the past participle for the verb flaw?
Well, to start with, flaw is not really a verb; it's a noun, and nouns don't have past participles.
Like practically any noun, however, it can be "Verbed" (as Calvin calls it; linguists call it Zero-Derivation, or Conversion), resulting in a causative verb to flaw, meaning 'cause to have a flaw'. It's not very common, though -- I mean, how likely do these sentences sound?
However, common or not, all Zero-Derived verbs are regular, and that means that the principal parts of flaw are
Draw and fly, however, are verbs, and are irregular, to boot. Their principal parts are
There are vowel shifts here, which is one mark of irregularity; the past participle inflection is another. The -n suffix for past participle goes back to Germanic. In Modern German, the past participles of "strong" (i.e, irregular) verbs always end in -en, while the past participles of "weak" (regular) verbs always end in -t. In English, regular verbs have collapsed both the Past and the Past Participle inflections to -ed, while irregular verbs vary all over the lot.
There's no more to it than what you've stated. The past participle form of flaw is in fact flawed, and never flawn. It's not uncommon for English verbs to have differing conjugations.