Try Alexis Malcom. She makes kilts from various military tartans including the Polaris Military. Last I heard, one of our members here - a guy who served with me on my boat (Will Rogers SSBN 659) - had ordered a kilt from her.

Tartan for a kilt is usually best bought directly from the weaver or from the kiltmaker. The kiltmaker can probably get better pricing simply because s/he buys regularly and has a relationship with the weaver. The kiltmaker will also make sure that you have the correct amount of tartan for your kilt.

Here is a detail from the kilt I made at my last class with Elsie Scott Stuehmeyer. When I ordered the tartan for my kilt from DC Dalgliesh it was to have been woven on the single width loom. There was a bit of a discount because I was taking Miss Elsie's class. Days later, someone (Alexis? don't know) ordered enough that my order, would be woven on the double width loom. Saved me a couple of more guineas.