We have always bought leather full size horse halters
at our local tack shop. We found the suckling size fits the smaller adult minis and weanling size is great for a little larger we alway get them with adjustable nose band. Our tack shop always carries exactly what we like and at a pretty reasonable price. I haven't found miniature ones it seems from a picture that I would like, but we have used the suckling & weanling size for quite a few years now. Maybe your tack shop would let you try a couple for size and return if you don't want them