Kromlech has some for primaris, also
IIRC old style marines.
Anvil also has some space marine stuff.
Mad Robot has some guard scale stuff.
Not sure on the scale of
these Maelstroms edge bots, but may be useful.
I suspect if you were crafty the imperial assault or similar star wars bots sets might be usable, but I've never bought one.
Probably some others--I could swear I remembered somebody making a plastic steampunk bot sprue, but it may have been just a suggestion floated I'm misremembering.