I’ve been using Sketch’s default iOS UI library, which uses Apple’s SF font. I already have a version of the SF font, but it doesn’t seem to be the same one Sketch defaults to. I’m sick of getting the missing-font notification. Does anyone know where to download the right version?
The only way to download Apple's San Francisco font is from the Apple developer website:
The font isn't licensed for any general use at all. Only paid members of Apple's developer program are allowed to download it and are only allowed to use it for screen mockups, nothing more.
If you aren't an Apple developer you're out of luck. You could get someone who is an Apple developer to download it for you (but that would be against the license too). There are other (non-official) versions out there, but as you have seen you'll get missing font notifications and have to replace the font, which isn't ideal.
Update: you no longer need to be a paid Apple developer to download San Francisco from https://developer.apple.com/fonts/, although the license hasn't changed and states only registered Apple developer are permitted to use the font ("You may use this Apple Font only for the purposes described in this License and only if you are a registered Apple Developer, or as otherwise expressly permitted by Apple in writing.").
Sounds like you already figured this out, but this is one of the top google results so I figured I'd post more links. Apple used to provide the SF font to anyone as normal font download, but now they only allow it as a .pkg installer supposedly just for developers. Even as a developer, I had this issue: "The San Francisco Pro Fonts installer does not allow its software to be installed here.
LINK TO GITHUB SFUIDisplay and SFUIText fonts: https://github.com/AppleDesignResources/SanFranciscoFont
HOWEVER!!! While these are the exact same fonts, the names are written in full. For example: Instead of SFUIDisplay-Heavy the name is SanFranciscoDisplay-Heavy
After installing, I still had to re-assign in sketch to use "SanFranciscoDisplay-Heavy" in place of "SFUIDisplay-Heavy"
Sounds like you already had that figured out, sorry can't get you better solution, but even though it's annoying, at least this works.
Go to https://developer.apple.com/fonts/ to download San Francisco Font styles as a zip file. extract the font files from the SF-Font.dmg then open the SF Pro file folder. All the fonts will be listing there. Then open the FontBook app on you MacOS. Go back to the SF Pro folder and double-click the file the font you are missing. A prompt will then appear from FontBook for you to verify that you want it installed. Once you confirm installation, the font will now be upload to your system. (Note: Might only work for MacOS systems.)