I have never seen this coin but a lot of promotional merchandise, medals and some "coins" have been sold over the years at the missions. However this is unlikely to be related to the missions as it doesn't have the name of a mission but King of Spain (Rey de Espana).
I suspect it is a real coin, of limited value given the year of issue . I am attaching a link to an article on Juan Carlos. You should check with a coin dealer if you want to pursue this.