As electricdawn already said, you can get copper and tin by making the trolls do the work for you.

I used to play with a potato laptop in the past and always skipped Bonemass because of the lag in the swamp areas, especially during fights. Finding silver with Stagbreaker is easy and after a while you start to kind of see what areas could possibly have silver. Finding iron is also possible with Stagbreaker, though it's a bit more difficult because unlike silver, iron doesn't give the "too hard" message, just "0". I guess I was lucky with my swamp, but I managed to find quite a lot of hidden iron. It seems to mostly spawn at the edges of the swamps, sometimes you can find several scrap piles relatively close to each others.