From the webclient 5.5 u3 I click the integration plugin link and I get the following error
An error occurred while processing your request.
Is there anywhere else I can get this?
Best to go ahead and download it manually. There are a lot of issues with this. You can refer the below link for details as well as download.
That page doesn't include a link to the .bundle file, it just explains why NPAPI support no longer exists, I am literally looking for the download link for the 5.5 u3 .bundle because the link through vCenter web is broken.