Since this is before they had a label, Amy Lee and Ben Moody stated in an interview that fans should simply download and redistribute these materials. There's no way to actually purchase them.
EvanescenceReference has graciously hosted these materials. Some are even available in FLAC lossless.
I'm not necessarily a fan of Evanescence, but I really enjoyed a lot of their pre-label material. I just can't get into anything beyond that. I figured I would share this, in case anyone has a similar interest in their demos and pre-label works.
For clarification, this is not piracy, nor the encouragement thereof. As stated, the band gave explicit permission to download and redistribute this material. It is not covered by a label.