Classic/Antique Car Repair: heater core, radiator shop, heater cores

Question
where can we find a 1959 heater core for a el-camino

Answer
There are vendors who run replacement heater cores on eBay all the time.  Just sign on to eBay and do a search for it.  

If no one has one running right now, e-mail the vendors and ask them if they have one.   If no one has one, you can remove the old one from the car and take it to any radiator shop and have them make you a new one - I've done that many times.

Dick