S-140 rims and tires

I have a 1955 S-140 with 9.00 x 18, 10 ply tires on 5 lug split rims that are in need of replacing. From what I'm told they don't make that size anymore and the cheapest comparable size is $400 a tire! I heard that military style 6.00 x 20 ones will fit and the tires are reasonable priced. Does anyone know if that's true? Or where I can find a set? Haven't been able to find a rim to measure bolt pattern or hub clearance.

Yeah, 18" isn't a size I've run across. Are these balls seat stud pilot rims? The nut is 1 1/2 acoss the flats"? if so I would think you could find some 20" rims that will fit that bolt pattern and easyer (but not dead easy) tires.

My S-140 had 20" Budd lock-ring wheels

Check out this link, found this guy the other day, expensive though
http://stores.ebay.com/CollectorsAutoSupplycom

these guys might have tires & rims
http://www.boyceequipment.com/tires.html

http://www.tyres1.com/Home.aspx

Ended up getting tires from these guys. They have a 10 ply 18" that is real close to the original size for a decent price. Included the link in case anyone else is looking for some.