Ofna makes foam tires that are supposed to fit.
Kyosho also makes some hi-performance slicks too.
Option Parts - Inferno GT
High - Performance tire for your INFERNO GT!
V-slick Tires are available in three different compounds, and are made from race-proven rubber that ensures long life (up to three times longer than stock) and better performance. The V-Slick Tires are packaged in pairs, include foam inserts and are designed to mount directly to any Inferno GT wheel. Wheels are available separately (shown for display purpose only). Three different shore ratings ensure these tires are ready for anything ranging from street or parking lot surfaces up to the high-traction of a prepared racetrack.
V - Slick Tire
IGT002-45 (45-shore rating) Soft compound
IGT002-55 (55-shore rating) Medium compound
IGT002-60 (60-shore rating) Hard compound