According to:
http://www.prime-mover.org/Engines/Lycoming/applic.html
the IGSO 480 was used in the following aircraft:
IGS0-480-A1A6 Beech Aircraft. Twin Bonanza (G-50), (H-50).
IGS0-480-A1B6 Beech Aircraft. Twin Bonanza a-50), Queen Air (U-8F).
C. Itoh.
IGSO-480-A1A6 C. Itoh.
IGSO-480-A1E6 Beech Aircraft. Queen Air (65).
IGSO-480-A1F3 Fuji T-3.
IGSO-480-A1F6 Fuji KM-2.
This company has them on their website:
http://www.coronacylinder.com/services.html
With:
IGSO-480 $37,500.00 (overhauled cylinders) $45,600.00 (factory new cylinders)
Aircraftspruce.com seems to carry some parts.