I would think your best bet is to do your homework and check NW and partners sites (DL, CO). Feed the search engines with the transatlantic portion first. A DL search may list AF flights as well. Once you find an option, search for the connecting flights separately with connections less than 24 hours (this is allowed on Int. itinerary). Within Spain you may be able to use Air Europa on the same award ticket.

There are just too many options to look for and many reservation agents either don't have the time to check them all or are not familiar with all the options available. The whole process works much better if you can give some suggestions and maybe tell them where you got stuck. Good luck.