Hello George
i think it’s worth remembering that a great many Samurai were “poor”. Being a Samurai did not equate to immediate wealth….often quite the opposite. The fine koshirae and armours that we see in films/exhibitions/books etc were in reality owned and worn by the very small minority of those that enjoyed a high rank and/or considerable wealth. It follows therefore that many koshirae, in fact the vast majority, appear to be of modest quality sometimes assembled from a variety of mis-matched pieces.
Also even a nice set of fittings (especially iron) can look pretty ordinary if neglected in a shed for more than 100 years.
….and these menuki are metal, most likely copper-as others have already said.