As pointed out in the question, the problematic tag-wikis came mostly from a single user. Since this user has deleted his account in the meantime, they can be no longer found through his profile page. (In case somebody wants to help and improve the tag-wikis which are still missing source/attribution.) 

To help with this problem, here are a few [SEDE](https://meta.mathoverflow.net/tags/data-explorer/info) queries which might help to find them:

 * [Tag-info edits by a deleted user](https://data.stackexchange.com/mathoverflow/query/885912/tag-info-edits-by-a-deleted-user?UserId=21574)
 * [Tag wikis created by a deleted user](http://data.stackexchange.com/mathoverflow/query/886143/tag-wikis-created-by-a-deleted-user?UserId=21574) 
 * [Get posts list of a deleted user](http://data.stackexchange.com/mathoverflow/query/405958/get-posts-list-of-a-deleted-user?UserId=21574)