Simple Question: Where do you download plugins?

I'm not looking forward to finding out the answer was in front of my face the whole time, but I've spent like 30 minutes just looking for where to download plg_gateway_sftp namely. I checked the plugins page, the plugins folder in the repo, my installation itself-- I have zero idea where to get this plugin or some of the others either. Could someone point me in the right direction? I know this is kind of a silly request. The support.filestash logs link didn't work and neither did the IRC chat link. Please excuse me using a Github issue to get this questions answered.