The other night I ordered a set of wheels from JC Racing in the UK.  As far as I know, they are the only company that produces a 2.2 wheel set that fits the original RC-10 without modifications.  This allows the use of modern rubber.  Even with the shipping from the UK, the set of 4 wheels just $18.

For now, I plan to buy a set of Proline Dirt Hawgs to run on the JC Racing wheels (just like the picture, but my wheels will be white).  If I run the car at the track, I hope to use the stock wheels and tires.  My true hope is that Proline or JConcepts will come out with modern tires that will fit the old wheels.