Pilgrim Passport for the Camino in Sarria, Spain?

Is there a place in Sarria (Spain) to pick up a blank Pilgrim Passport or do I need to go out of my way to a big city cathedral to get one? I plan on taking the night train from Madrid to Sarria and start walking towards Santiago de Compestelo from there. I've set aside 5 days to do this. What do you recommend?

Sarria is about 100 k east of Santiago and about 25 k east of Portomarin. It's south of Lugo.

There are several towns by the name of Sarri谩 in Spain: one near Vitoria, one near Lugo, one near Bilbao, and a fourth one Sarri谩 de Ter near Girona. Which one are you referring to?.. Once you add that information I'll be able to give you a fair answer... Also if you know the distance between the Sarri谩 you refer to, and Santiago de Compostela, it would also be helpful.
:-)
OK...with the added info... You can get the "Credencial" at an address in Lugo that you will find at the following website:
http://www.caminosantiago.com/index.htm
For it to be validated you have to do at least 100 kms. on foot, bike or horseback and have the credencial stamped at each stop you make on the route, either at the local parish or pilgrim association office ...

I hope you enjoy the experience... I have family who have done the road, and say that it is a wonderful feeling, the comradeship, self satisfation, healthy exhaustion, etc. All worth the effort!