Yes, there are psd mockups available, however, there are many downloads that are marked as "mockups" or appear when searching for mockups, but the files that are linked are jpegs or illustrator files which are not user friendly (I would argue they aren't mockups at all) and a waste of time to download. Example: I type in "T-shirt mockup" and the vast majority of results are ai/eps and jpeg, vs PSDs with layers and smart objects, which is what most people are looking for if they are searching for mockups. On CreativeMarket.com if I type in "t-shirt mockup" the vast majority are layered PSD files with layers and smart objects. I also find it extremely irritating that there is no way to filter results by psd file type. This would eliminate seeing unwanted results for any search, mockups included, and downloading useless files. Most competitors have this very basic search/filter option and it is surprising that Adobe doesn't.
If you are looking for editable mockups, then search in templates, where you can also filter for Photoshop.
This can be done two ways–filtering to templates while in the all context or changing the dropdown to templates. Here’s the link example for the latter with the photoshop filter applied. https://stock.adobe.com/search/templates?filters%5Bcontent_type%3Atemplate%5D=1&filters%5Binclude_stock_enterprise%5D=1&filters%5Btemplate_type_id%5D%5B%5D=1&k=tee&order=relevance&safe_search=1&search_type=filter-select&get_facets=1