I’ve used dwarf bucklers for my fireglaives and the one half of the marauder drum for my handweapon guys. See my blog for pictures.
The marauder shoulderpads are pretty cool - all kinds of evil. If you want something that looks like uniform, you could go for some spavemarine shoulderpads. There are loads of cool shoulderpads from GW and FW. I’ve been using world eater (the pad has some cool spikey teeth) for my chaos blood bowl team. It works well - even for warhammer.
Great idea! Consider it stolen. I just ordered some chaos space marine shoulder pads. I’ll have to decide whether to use them as ironsworn or use them a blunderbusses. I’m leaning towards the blunderbusses.