As far as I know, there have been three new weapons added to damage Wights/Walkers, these are;
Dawn, the sword of house Dayne, which has existed in game for a while but has been updated with 7.0 to damage Wights. This sword can be found just as before in Starfall.

Lamentation, the Valyrian steel sword of house Royce. In lore the sword was lost during the destruction of the dragon pit in King's Landing. I haven't managed to find it yet so it would be appreciated if anyone who has could let others know in the comments.

The final new weapon is the Valyrian steel sword Red Rain, held by house Drumm. The sword is carried by Dunstan Drumm and can be aquired by either sending him to the wall or executing him.