You can easily do them yourself if you can use electric jigsaw. Just buy new plastic hubcabs, cheapest you can find. Take the inner part off to save weigth. Saw a round plate in correct size from abs sheet. srew the round plate with 5 screws to the outer edge of that original hubcab. Better instructions can be found here if you use search button.
Cheapest place to buy that abs is propably companies that do vacuumforming. They migth even give them for free if you say where you need it
.
ABS costs about 3€/kg on sheet material. If you buy one big sheet you can also do airdams and ballypans with the same material
. I would buy 3mm or 4mm thickness.