Most small engined cars are faster on the 13 inwheels. VWs are for sure. I have bought entire cars to get 13x6 wheels. I have one good set after 20 yrs. of JY shopping.
Can you buy Basset 13x6? yes. About 60-70$ each.
Does Tire rack sell them? no.
15x7 are far easier to source, 205/50/15 are the best tires to source. (Other than the SFR tires thatI use.)
I think that both sides of this point are valid. The old cars have scarce wheels. The new builds may need to buy steel wheels or Panasports.
While the choices are slim, there are choices for 6 in wheels.
Maybe "Prod" them in, Add 50 # for 7 in wheels. No wider.
MM