As far as I understand from what I have read on your post you don’t have currently any administrator, thus the president must hold the offices of administrador and secretary in accordance with section 13 (5) of the HPL
The functions of secretary and administrator shall be exercised by the president of the commonhold except when the Articles, or the Owners’ Committee by majority vote, provide that such offices be held separately from the president.
Section 20 provides for the major responsabilities of the administrator, one of them is:
20 (e) To act, where applicable, as secretary of the Owners’ Committee and to keep custody of commonhold documents available for the owners.
If your president-secretary-administrator refuses to provide the contact details of every owner in order to send a notice calling for an EGM you should arrange a “requerimiento notarial”
If the president still refuses section 256 of the Civil Procedural Rules provides for pre-trial proceddings
256 (1) Every trial may be prepared
(4) By a commonholder’s request to show the community documentacion
The problem is that you are seeking that information not in order to call for a meeting but in order to obtain the support of the 25% of the owners, thus the president could deny the request under the aegis of the Protection Data Act.