The reason you don't see that many big fish in "private" aquariums is because most of the people kill the creatures they pretend to care for. Myself included in that statement. I have had a few fish that died for no obvious reasons, so I have nothing else to blame but myself for doing something wrong. Then even if there was an obvious reason, if it was bad water parameters or something like that it would be my fault.
I don't wan't to get into it, but basically if a specific species of fish doesn't reach it's average size (Within reasonable variance) then there was most likely something wrong with they way it was cared for.
Eels grow very fast, even on a twice a week diet you could resonably expect to have a 1' green moray become 2'+ in it's first year. So to suggest you will have a tank ready for him at will is not realistic. And a 4x8 (foot print) tank would not be big enough past the 4' mark IMO. These eels love to swim and explore and would be far too cramped in that tank.
Now, the Dragon eels at 3' max would be better. My braziallian has been great, got him locally for $120 which is a deal. I have seen them on liveaquaria.com as well as Marinecenter.com A bit pricey but a reliable source for fish.
You should be able to also ask your local dealer to just order one from his supplier.
My whitemouth eel was 12" when I got him 2 months ago and is now over 2' long. The dragon was about 1.5' a year ago and is now a good 3'. Also have 2 zebra morays that are about 3' and 4' in length (they actually grow slower than the rest). The golden tail moray are very nice eels and stay under 2'.
