I feel your pain. I made almost that exact same mistake (boots in the summer) two years ago, and sent almost this exact same request. Went to Base at Calle Madrid 19. Ended up with a pair of Asics tennis shoes. Not perfect, but they got me to Leon, where a store had a pair of Keen Newports in my size, and another store had a pair of Merrell water shoes (??? Hey, they worked for the asphalt and concrete better than the Keens).
Get your shoes, then go to Michelle and Felix's alburgue in Rabe de las Calzadas (Santa Marina). A bus will take you most of the way, but you'll have to walk the last 2km (the most painful 2km of my life). Beg Michelle to fix your feet, even if the alburgue is full (there are only 8 beds). She fixed my feet, but more importantly my spirit (I was ready to quit the Camino). She said that if I just walked as I could (leaving at 6am to walk in the cool of the day, changing socks every 45 minutes, lots of footpowder) I would get to Santiago. If I could not walk more than 10km a day, that was fine. I would still get there. She was right. The Camino breaks everyone. And it put me (and many others) back together again, as long as I did not give up and kept walking). The lesson I learned is that we do not heal and then do life. We heal as we do life. Don't stop walking.
Buen Camino,
Jo Jo