It’s not perfect, but the UVs here should be decent enough for previewing or texture painting purposes. Free to use, no credit needed. I spent ages looking for one of these and did not find what I was looking for; hopefully this reaches at least one person who finds it useful.
A small note: The topology here differs slightly from the base model; specifically, certain edges have been subdivided around the corners of the model to allow better mapping.
RobloxianClothingDummy.blend (1.2 MB)
RobloxianClothingDummyR15.fbx (132.6 KB)
RobloxianClothingDummyR6.fbx (63.0 KB)