That is the major problem with them. My only suggestion is to ask your LFS. Mine was fairly good about finding some and I've seen 3 species in the last 6 months at LFS's. Their not uncommon just not as often collected as more common species.
This site appears to be selling what is definitely not a banded snake eel. https://azgardens.com/product/banded-snake-eel/ So You'll need to be wary of fakes too.
This site also has one but I know nothing about them so buy at your own risk I guess: https://violet-sea-fish-and-coral.myshopify.com/products/banded-snake-eel?variant=39717587091527
Divers den occasionally sells snake eels though its usually the relatively aggressive but easiest goldspotted.
Thanks for the tip! My LFS called today and finally got one in for me. A banded snake, although a little longer than I had hoped at ~2ft. Going to set up an observation tank with a deep sandbed/some pipe and hopefully get him settled this weekend. Then will have to figure out how to introduce him to the DT without freaking everything out (including him).