By Brian O’Connell Screening for stocks trading below this key metric can uncover big opportunities. Looking for profits in all the wrong places? Real Money Columnist Jonathan Heller has an idea. One of Heller’s favorite hunting grounds for smaller potential deep value plays are “net-nets,” or companies trading below net current asset value (NCAV). “It was once a unique place to find down-and-out names with the potential to offer compelling returns,” Heller wrote on Real Money. “These opportunities have dried up for a couple reasons, one being the overall rising tide of the markets in recent y…