Great question! I'm not familiar with any sites or organizations in Spain that highlight accessible housing or communities. I would say that major cities would be the most accessible - Madrid and Barcelona. Smaller towns may be accessible in some areas but overall I find much of Spain was not built with accessibility in mind (except for the visually impaired). Most new buildings will have elevators but the units themselves may not be wheelchair accessible. Buses are wheelchair friendly but not all sidewalks are. I hope this helps!