I'm wondering if there is a way to access the working sizes of the official subeta pet art.

Most artists upload the images to their tumblr or deviantART accounts. If you go to either of these websites and search for the pet species and color you might be able to find them. (Or by knowing what artist drew what and going directly to their account to search). Not all pets have had their working sizes uploaded and you might have to ask the artist directly for them to put it on.

The subeta tumblr often reblogs the artist's working size images so you can probably find the artist's blogs through there (and most of the working size images directly from there)!

Thanks a bunch guys :) Will check it out