How can I keep my IR currency outside the USA?
The easiest option is to find a US CFI/AI holder in the country you are in, to sign off on your approaches.  It might be allot easier if s/he is also a Spanish CFI particularly if you are flying in a Spanish registered aircraft.  You do not indicate if you hold a certificate from Spain.

It is not uncommon to find instructors with US FAA CFI ratings in other countries.

There is no prohibition of a US CFI giving instruction in another country.  There may be of a given country, or operational limitations imposed by aircraft registration, host country operating rules, and insurance limitations, as well as owner / lease limitations.  

However, I routinely sign off US pilots for approaches made at Canadian airports, in fulfillment of their US instrument recency requirements.