Anyway, I don't think you have any problems in Sahagun to obtain your credential.
If you spend some time in Madrid, you can take it in the Madrid's Association.
C/ Carretas 14, 7, B-1 (Metro Sol) 28012 Madrid
On tuesdays and thursdays (19:00 - 21:00, all year)
and on wednesdays (11:00 - 12:30, closed on july and august)
Buen Camino,
Javier Martin
Madrid, Spain