It's going to be tough buying these used. They're pretty rare tanks. You might want to try reefcentral. They have an Elos forum.
If you want to pay for a new Elos tank, you can try the website they have, or give Manhattan Aquariums a call.
Or.. If you have some DIY skills, you can buy a Solana tank, remove the back wall, get the tank drilled, and install a custom "Elos style" overflow. (Yes, I was 90% there once, but decided to sell the tank instead)
Yes, i actually hit up the ELos forum there definately doesnt hurt to post in both places. If i cant find one within a month or so i would seriously consider a solana mod. I love the clean lines of the Elos where you can see from all sides.
Anyone ever tried using natural sunlight in the daytime? I was going to park the new tank (if i find one) in the corner next to one of my floor to ceiling windows which should give me a fair bit of sunlight during the daytime.