I am not sure where you could get them but I bought some from Lidl that are ace for skinny legs, lots of velcro straps (not just the normal 3) and waffley on the inside so grippy and not overly sweaty.
Poly pads travel boots are only ones that fit my twig legged TB, or I bandage for long journeys. I got set of PP boots,barely been used, for £10(Inc the p&p!) off fleabay.
It might sound silly but there are people on ebay who sell travel boots for miniatures. I have some and they are great. You dont get much skinnier legs than miniatures! Why not search a seller and ask them if they can make them longer?