Gunbroker.com occasionally has NEF barrels but not often.
They have a better policy on bidding, in my opinion, if you place a bid it will wait 15 min before closing the auction. In other words, the auction has 45 seconds left and you put in a bid and take the high bid. The auction will extend itself for another 15 min. This keeps the snipers from winning all the time and allows the highest and fairest bid on it.
Don't get me wrong, I have "sniped" before but their system is more fair overall.