A "full service" hardware store will have generic lawn mower wheels in 6", 7", 8" etc. I find these fit and work fine on Lawnboy axle shafts. Not for the self-propelled though.
Wheel bolts make the wheels wobble,and ebay has a new set of steel wheels for $52.50. I put a set on my 7227 ,1977 Lawn Boy ,with new bolts.Also,have 5243,4502, 5243 restored ,finished today,started first pull,and ajusted carb. purred.
You probably won't find new green ones...And if you do you can expect to pay a premium.
Depending on the condition, you may consider drilling them out and installing bushings to tighten them back up.
Lee