'sawn' is losing ground to 'sawed'. This is the way of language. The "new" rule [that's been around for centuries] that ENLs have in their brain is "the past tense is made by adding "ed". Irregular verbs, though still quite individually strong, are fighting a losing battle.
Results 1 - 10 of about 655 English pages for "have sawn".
Results 1 - 10 of about 9,850 English pages for "have sawed".