Sara - what jobs/dates etc did you put down on your original application? I'd presume these would be fairly accurate?
I've called up my employers from the past few years and they've all sent things to me.
Point to note re. Australian Taxation Office - unless the companies name was lodged on your tax return, they don't keep those records on your return (they take what you lodge as truthful, until proven otherwise) so, whilst you can rely on the ATO to send you proof of payment (your notice of assessment) they cannot show you who you worked for.
But, when you applied, EasyJet told you you needed all of this info anyway?
I'd move on it fast, start calling the temp companies, they keep records, by law, I believe, up to 5 years.