Non GW figures that scale with Cadians etc.

[Sir_Theo]

If you can wait till September the newly announced collaboration between Wargames Atlantic and Reptilian Overlords looks promising. First set are basically Catachans

[Pattus Magnus]

I’m sure any resemblance to Catachans is entirely coincidental. They do look like they would make reasonable proxies, if you used your imagination, though. 

[KGatch113]

If you can wait till September the newly announced collaboration between Wargames Atlantic and Reptilian Overlords looks promising. First set are basically Catachans

The bare arms kill me on those. I'd need to find sleeved arms. I think Mad Robot has some that might work.

[frank xerox]

Void have some jungly types in their viridian range, some of syntha might be useful too. I reckon they would fit scale wise