All lithium batteries are now classified as dangerous goods and cannot be carried by air.
Australia Post cannot accept lithium batteries or devices containing lithium batteries for mailing overseas or for domestic air carriage. Parcels containing these items will now only be transported within Australia and by road only."
Not sure about actual sources, but it seems that a few "vaping" suppliers stock the eFest 3000mAh IMR 26500s; these seem about the best "known/tested" available at the moment? The ones on DX, Fasttech etc still seem to be unknown quantities; the "5000mAh / 5500mAh" ones seem to be reviewing as only about 3000mAh if that, and no known supply/quality consistency