Some thoughts - the tartan hose with the seam up the back may have been knitted on a knitting frame, such as was used in the 18th c. and into the 19th c. The hose was knitted flat with the leg contours on each side, and then they were joined together in the rear and on the foot part by sewing them together - ergo the back seam. I don't know if anybody still has such skills or knitting frames - Colonial Williamsburg in Virginia is the only place I've ever seen a knitting frame and I don't know if anyone there practices the art. The good folk there might be able to steer you to a modern day craftsperson that does frame-knitted hose.

As to hose made from tartan cloth, I've made about 15 pair (for living history purposes) from tartan cloth. The 18th c. Highlanders were reported to have worn hose made from tartan that was of heavier weight than their plaids. I cut mine on the bias and sew them together with the twill lines vertical - this gives them lateral stretch. As to the part of the hose that fits around the ankle, I have found that it must be somewhat loose in order to get the foot through without doing damage to the seam. With a little experimentation/fitting, I've been able to size my hose so they are fairly close-fitting around the ankle while still being able to get my foot through that part. The most difficult part (for me) of making so-called "bag hose" is getting the pattern to match in the back where the seam is - I've never succeeded at it, although I've come close a few times. I would not hesitate to wear properly fitted cut-and-sewn hose with modern Highland formal wear. It is traditional and the major cost is your time and effort - not major money.