I have a Zodiac, but many wheels will fit any boat of about the right size. I bought my boat from Central marine Services...
Central Marine Services
... and they sourced some excellent wheels for me much cheaper than the Zodiac originals. It may be worth giving them a ring. They are very helpful. The wheels they sold me are on stainless legs and have pneumatic tyres. I see no reason why they shouldn't fit almost any small-medium RIB.
What can say, after owning 3 SIBs is that there is a HUGE increase in convenience for adding even the cheapest wheels, and an even hugerer increase in convenience for adding a decent set of wheels.
A boat that is a pain in the backside to use is a boat that may not be used. Shop around but if necessary, spend the money.