Silver? Meh, that isn't so hard to find, but finding the vegvizer to Moder, the mother of dragons... that will make finding silver simple by comparison ;)
I had to search 11 mountain ranges, over half of which had silver, before I found the right one. The right one is a mountain that is HUGE and makes all other mountains seem like molehills. The good news is, when you do find it, you can't go wrong... it will have wolves, skellies, drakes, golems, silver and the ritual site you'll eventually use to summon her.
Keep looking and good luck ;)
https://steamcommunity.com/sharedfiles/filedetails/?id=2414139080