i've found out YouTube is arguably the best source for "natural" pose references.
make a Playlist and look up things like "martial art". Build up as big a library as you need and use it as a point of reference.
You'll find a lot of masters and martial art content in there. a lot of high quality videos too (tip: play videos at 0.25 Speed)
one channel i really like is Master Wong. Very skilled and VERY funny XD
or Senshi Stock
you might also wanna checkout Bodies in Motion
https://www.bodiesinmotion.photo/