On a spacious terrace in Brookline, a group of 30 women sip wine and dine on salad and sirloin. Dressed in suits, slacks and colorful frocks, they could be members of a book club, a garden club, or an offshoot of a PTO. But talk doesn’t revolve around kids, weeds, or reads. “I am looking for a level-C co-founder,’’ said Tara Cousineau, of Milton. The woman next to her nods and goes through her mental Rolodex to call forth a few names. At the monthly meeting of the SheEOs, a diverse network of female CEOs in Boston, help comes in many forms. “You’ve heard of the old boys’ network?’’ says Bettina Hein, founder of Pixability, a Cambridge-based video marketing company. “Well, this is the old girls’ network.’’