Are you looking at buying an upright ("true" mini sprint) or a sidewinder? The tracks listed above run strictly sidewinders, with US24 running special upright (1000cc) non-wing shows a couple times a year. It seems as though Bakersfield (Linton) is the only track running 600 uprights on a regular basis. MMSA allows 600's to run aginst the 1000cc cars with a weight break, but almost every association and non-sanctioned track running uprights in the area have gone to 1000cc.
It's not a hopeless situation though; I've seen a 600 upright from Bakersfield beat a field of 1000's and 1200's in an open non-wing show at US24.