I got it from the author's (Smorodsky) github account, but it must have been corrupted on download. I re-downloaded (https://github.com/smorodsky/Select/archive/master.zip) and it now says the following upon double clicking to install into extension manager:
The author explained how to work around the issue:
To manually install:
This worked to get the extension working for me. However it does not show up in Extension Manager.