tapas in spain
The idea of reservations is kind of antithetical to eating tapas in Spain. You can probably find new-fangled "small plates" type restaurants in Barcelona and Madrid, but this is not the traditional or typical format.
I'm sure a good restaurant will be happy to feed you "raciones" -- plates of usually simple food, such as ham or cheese or boquerones or omelettes or simply prepared vegetables, as opposed to entrees.
But tapas bars, even very upscale ones, are an informal afair. You just go in an stand at the bar or find a table and order what looks good -- or sound goods if they have a written menu.
I agree with the above post that traditional tapas places are informal affairs where reservations are unheard of. Everyone just cramp in to eat, chat and drink. There are small plate places that will take reservations but for me they do not offer a true tapas experience. In Barcelona, Paco Meralgo, Cal Pep (for the back room/not the counter), Comerc24, Santa Maria. In Madrid, Bocaito might take reservation in their back dining room. Can't think of anything in Girona, but do consider El Celler de Can Roca for an upscale restaurant if you have not.