I've gotten ores from Wyvern skin and Dragon skin both if that helps. I haven't gotten any shells yet that I can recall though.

From reddit, if I recall correctly, Wyvern skin were reported to drop ore and shells and dragonskin just ores. I didn't see anything about the other maps. I assume the other heavensward ones probably drop something but maybe less often. After doing maybe 20-30 each of the wyvern and dragon, it seems getting ores out of dragon is the easiest, but of course you need probably 2 or more people, which means, more sharing (but people can work it out usually to be fair).