Raise descriptive error if a distro can't be found

[MHendricks]

Raise a descriptive error if a distro can't be found instead of a generic KeyError.

Checklist

• [x] I have read the CONTRIBUTING.md document
• [x] I formatted my changes with black
• [x] I linted my changes with flake8
• [x] I have added documentation regarding my changes where necessary
• [x] Any pre-existing tests continue to pass
• [x] Additional tests were made covering my changes

Types of Changes

• [ ] Bugfix (change that fixes an issue)
• [x] New Feature (change that adds functionality)
• [ ] Documentation Update (if none of the other choices apply)

Proposed Changes