To locate the volumes of the Patrologia Graeca on Google books, use the search “cursus completus series” (without the quotes). To get volumes of the Patrologia Latina as well, leave out the term ‘series’. NB: It is important to specify “full view”, otherwise nothing much comes back. I’ve today seen what seem like dozens of volumes of the PG. I’m not sure whether these are visible to US readers (I’m accessing the site via a multinational’s WAN which makes me look as if I’m in the US), but I’ll add a note if this is a problem.
I find that the online displayed copies often seem to be missing pages; but the PDF available for download for them all does not.