Right now we can forge 6 items, so my plan is to hide at least 2 more throughout the game in future updates (likely in side content).
Lianna's top tier staff and robes aren't made of mithril, but I may or may not hide a mithril bangle somewhere. (And no, mithril bandanas aren't a thing lol)
Well earrings are more of a Shida thing (as he already wears a mithril earring by default). Tho honestly I'm considering making a scarf item and fix it to Mao's head slot (like Lianna's hat) for the final version. Not sure yet!