BBVA, Banco Popular, and Caja Madrid (now Bankia) offer Iberia Plus credit cards which let you obtain points.
AMEX will also let you transfer Membership Rewards points to Iberia.

Iberia does have several retail partners, such as Cortefiel for instance, however the point obtention is very low.

You can see a list of all their partners on their web site. They do have quite a few.