eBay has been eliminating many small categories in favor of using fewer, larger overarching categories and employing filters to select various item-specifics to accomplish much of what the smaller categories were used for.
For instance, there is a "OOAK" item-specific under the Features filter in the Doll categories.
There is an "Artist Doll" item-specific under Doll Type.
"Polymer" and "Clay" are options found under the Material filter.
To see all the filter options within a given category, scroll down the left side of the search results and use the "More filters" link.
If you cannot find an appropriate item-specific, you can always try searching using that term as a keyword:
https://www.ebay.com/sch/i.html?_from=R40&_nkw=ooak+artist-doll&_sacat=262346&LH_TitleDesc=0&_fsrp=1
If a keyword is found in title or the item-specifics of a listing, the listing should be returned in a search using that keyword.
