I'm going to be perfectly honest (as the self-appointed designated MMD idiot in this forum), I don't have much of an idea. If you want something custom-made, it's gonna have to cost you cash. Otherwise, you'll need to DIY.
There's of course the method of taking other peoples parts and putting them on a base, but that can make your model end up looking generic, and could cause issues if you aren't very careful to read the readmes.
If you're going to do the doll-costume part with a base and clothes, there's going to be many issues for adjustment. Hell, when I tried using a base, I, no joke, just recoloured the skin texture.
Right now I'd suggest, if you're unable or unwilling to spend the cash, and you really don't have the mind or patience to do it yourself or even use a base and other clothes
(using bases is something I'm personally against btw), then all you really have it to you is to just keep working on your UTAU in terms of quality and promotion to generate some sort of interest. Perhaps there's someone else around here that has half a sense of modelling capabilities which you could do trade with, if your time and skills is worth theirs.
Really wish I could actually help you but when my most complicated model is best described as a blocky enviroment with some oddly morphed spheres to act as small rocks there's not much I have in terms of modelling skillset.
All in all, there's a sacrifice in everything, whether it be money, time and lifeforce, or personalization.
When it comes to vroid, if you wanna
turn that into an MMD model...
the bowlroll search part failed on me for the first time, but it's there, somewhere, somehow, not gonna share the link directly.
If, a couple years in the future, it actually
does dissapear, I'll have an archive of it.