I've managed to get my hands on a few sets of artillery wheels the last few years.
The first set are resin pieces that were enlarged to fit the 41 Lincoln kit tires. These came from Drag City Casting(Ed Fluck), and I'm nearly positive he has discontinued them.
The second set i found at a swap meet, but they were still listed on a showcase hobbies website or Facebook page recently. They are normal 1/25 size measuring .605" where its going through the wheel and .650" at the wheel lip. Pictured in a tire from an AMT 32 Ford kit tire.