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