Dana, I don't know if anybody is making the bases in 1/32 but you could combine 2 or 4 of the 1/48 possibly. Or even make your own, I've made a couple of smaller diorama bases using Durham rock hard Water Putty as a coating, doing my best to keep it smooth as I applied it but sanding it down if need be when its dry. Then you can either paint it or use a product called Road System Top Coat, Asphalt St1453 from Woodland Scenics. This stuff is water soluble so you can thin it and brush it on, it ends up looking awfully close to paved surface. Hope I helped.
Bob