Hence my MC cable suggestion. Might be more available than SE, and it comes in 6/2. (Whereas 6/2 SE and 4/2 NM don't exist. Which maybe should change.) 4/3 just really seems wasteful given both bigger conductors and the extra conductor. (I know, NM is easier to work with, but still...)
You could also run FMC and pull, depending on the site.
These issues aren't going to go away, they're only going to become applicable to more and more of your work. Start telling the supply houses if they don't stock something better for these applications you'll order online.