Festivals all over the place, not all on the Camino Santiago. You might look up the villages along the way and find out when their local patron ferias are. Here are some I found online:
– San Froilán in Lugo. From 4-12 October for a week. Camino Primitivo – Original Way. León, on the French Way, also celebrates San Froilán.
– Fete de St Foy in Conques, on the Le Puy Camino, in France. Around 10th and 11th October.
– San Lucas horse and country fair in Mondoñedo with origins dating back to the 12th century. Mid-October. Camino del Norte– Northern Way.
– Apple Fest takes place in Redondela, on the Portuguese Way, in early October.
There's an Irish festival in Cáceres on October 25
A couple of saffron festivals in Toledo October 25-28
The Pilar fiestas in Zaragoza from October 5-13
October 18-28 is a floral festival in Córdoba
Valencia has a local festival starting with fireworks the night of October 8
Wine festival October 10-13 in Cangas del Narcea, Asturias region
Fiesta of the Moors and Christians in Crevillente October 5-7
Oktoberfest in Madrid on October 24-27
San Lucas Fair in Jaen on October 12-20
Concurs de Casell (where they build those giant human towers) in Tarragona Oct 5-6
White Night Festival October 5 in Madrid - free entrance to museums, etc.