Like Jirka says, cut the outer ring of the inner part and lower the new ring a bit.
But You can also go for Turbo Optima wheels, here You´ll find narrow fronts.
Rear tires - If You´re willing to pay 50 usd, You should be able to find a set
I had the same problem as You, 4 sets of narrow fronts and no rears. I found some 2,0 tires called dirt paw with the same tread pattern. Here´s what they look like: