Amazon and such, order online. For Instance I use THESE off Amazon. You can check the Amazon store page for Doc Miller to see the other options they have.

I couldn't stand full hose/tights style, though it's the best as it also provides compression to your lower abdomen as well, so I went with that type.

You want to get multiple pairs, and after every use you want to wash them in cold water, gentle (or hand wash cold), air dry, no heat. This keeps them effective for the longest, heat will ruin the compression.

I have a half dozen pair and I have to replace them every year or so depending on how frequently I've worn them.

If ordering online, order a single pair first in case they don't fit correctly, and from some place that offers free returns (like Amazon Prime).

Alternatively there are also places that can measure you for custom fit leggings or hose, such as some medical supply stores, but those are significantly more expensive. And there are online sites (just search for custom compression garments). Some insurances might cover them with a prescription from your doctor.