Hi!!!
I live in Barcelona and moved here with my children some time ago. I also needed to fine information so that they could continue with the activities they did back home and as soon as I arrived I went to the “Ayuntament”, the city council, and they provided all the information I needed. You may try that!
However, my daughter practiced football for a while here and I will try to call her couch to see if I can find out about football clubs in Tarragona and send you the information.
Good luck and welcome to Spain