Thanks IrishGunner
This is the website for the archive in Alcala, aka the AGA (in Spanish): http://www.mcu.es/archivos/MC/AGA/index.html The archive closes at 2.30pm and they don't allow photography so you have to make the most of your time there.
From memory, the file with details of Medalla de la Paz recipients was under the catalogue heading of Africa 15(3) or Africa 15(17). If I can find more details, then I'll post it here. Unfortunately the AGA only has paper index files on-site so there's no way of checking the catalogue without visiting the archive itself.