I don't know if you can just get the caps, but here's what I did. A buddy ordered a green cap battery and got a yellow cap battery, the CO. sent him the correct green caps for the repo battery he ordered and he gave me the yellow caps.
I took the yellow caps and ground down the threads so they would push into my Interstate battery. I am very pleased with the look but I have a MTP-24 ( MTP is a high cranking amp battery ) that has Interstate molded in the top, when I replace this battery I will order a MT-24 that only will have a Interstate sticker on top and once removed I will have a solid black case battery with the correct yellow caps for my car.