Hawkins & Powers, the aerial fire-fighting specialists in Greybull, have put much of their large fleet of vintage warbirds, converted to "fire-bombers" up for sale.
Their web site does not have many details:
http://www.hawkinsandpowers.com/sales_fixed_wing.htm
A bit more information is on the Courtesy Aircaft site:
http://www.courtesyaircraft.com/
Two PB4Y-2's are listed at $ 550K & 800K.