This is a tough one, because as you know, it is not economical for most brands to carry sizes that small. However, you should check out Suit Supply, BB Black Fleece and Thom Browne, as they carry and use smaller cuts. Some Japanese brands also use smaller templates for their clothing. Other than that, you should go made to measure - there are many options popping up that can make you garments for cheaper than ever before. Finally, don’t be afraid to look in the adolescent departments as well - I have friends who cop kids stuff all the time as the fit is better and the clothing is cheaper.