need somber smithing stones from 1 to 10 , need two of each

You need to farm for it.

Cant u drop them while coop?

Find bells you can give them to the fingers merchant at the roundtable and then buy as many 1-9 as you like.

I have 1-4 & 7-8 available ti buy at the moment.

Honestly there are so many good weapons that will carry you through the game I wouldn't even bother buying anything with fg

Can't drop them, but people can take your weapon and +10 them for you.

I could be wrong, but when I tested trading upgraded weapons it would not work. Only non-upgraded/vanilla items were tradable.