T.D.
Do you speak Spanish or Catalan? Simply go the kiddie parks in the afternoon and start talking to the other moms.
If you only speak English, ask your husband if his co-workers have English-speaking spouses. I just googled "english speaking playgroups in barcelona spain" and got tons of responses...at least a place to start. Contact the American school or the Benjamin Franklin School (if memory serves) and ask them if they have a PTA contact who might have info for you. Start asking about Kindergarten registration...certainly you'll meet many moms like yourself there.
**Don't even bother with the American embassy or consulate...they don't do social networking. 17 years of living in Spain and attempting to get ANY sort of help from our State Department there has taught me that you simply cannot expect them to help you...Citizens' Services is a total farce.