Doubt if you will get imperial to metric plumbing fittings out here, Spain was metric long before the UK.
Looks like you are after plastic drain fittings, you could try to get the closest metric fittings and glue them to what you have now with plastic pipe PVC glue.
Here in Spain, all plastic fittings are glued, the type used in the UK that push together and are sealed with rubber rings, are not available.
There is good place on the right on the way into Los Montesenos from Quesada that have a good selection of fittings.