I haven't checked the schedule for these shows so I'm estimating dates, but you can look each up online. Unless otherwise noted, all classes of cars participate.
Wheels and Waves in Santa Barbara around April each year. 400+ cars
Wheels and Windmills in Solvang (date ?) 300+ cars
Lompoc Police Dept/Special Olympics in Sept each year. 170+ cars
Los Alamos Old Days around Sept/Oct each year. 150+ cars
Kalifornia Kustoms in Santa Maria around May/June each year. 1500+ cars mostly custom.
Pismo Beach Classic around late June/July each year. 700+ cars
Arroyo Grande.... (date ?) each year. 500+ cars
Atascadero Hot August Nights. 300+ cars
Many smaller shows in Morro Bay, Cambria, Lompoc, Santa Maria, Orcutt, San Luis Obispo etc.
Avila Beach Concourse De Elegance (date ?, annual ?, number cars ?) Many fine vintage domestic and foreign.