Evo used “... some old WFB bare dwarf arms ...”
You could ask for more info on his blog, but I imagine they came out of his bits boxes and he wouldn’t be able to give a more specific answer.
Inquisimunda modellers use all sorts of plastic bits and pieces in their conversions, but they often have to trim, reposition and fill things.
The Uscarl arms, weapons and equipment are metal, BTW.