Where to get Initial EASA Class 1 Medical?
It depends on the country you are going to take the medical examination.

Normally, the national civil aviation authorities of each European country will have this listing. For instance, in Spain, AESA publishes here the approved medical centers where applicants can take their initial and successive examinations.

So I suggest to first find out the authority from your country and always make sure with the medical center that you are going to take a certified EASA Class 1 medical examination.