You can use any of the mini suppliers listed in other threads. Minis are on their own roots. You'll want to buy varieties that are hardy in your area.

Here is a link that might be useful: Where to purchase mini roses

Michigan Miniature Roses was highly recommended to me by the owner of another miniature rose company who I was friends with. It's just over in Belleville, but it is a mail order company with a good selection and their roses should be hardy for you. I hope they're still around.