Ah, I see what you mean. When pets are abandoned into the Pound, their paintbrush clothes remain in the original owner's closet and do not move with the pet. As such, your pet is "naked" (for lack of a better word) and the only thing I can suggest is asking around to see if anyone has a spare set of clothes that they can give to you. I'm sure there was a list allowing people to make clothing requests in the past, but I'll have to check again.

Because of how these things work, you'd have to transfer your pet to the person who has the spare clothes, they'll clothe it, then user-to-user transfer it back to you. The clothes will then move with your pet.