http://www.keyboardco.com/ sells the Filco Convertible 2 [0] and a few other Filco keyboards - they also ship internationally. Bought from them before, would definitely do it again.
Hi! Doppins is free for open-source (and currently also private) projects, but I get your point.
What I like about using Doppins on my own projects is that I don't have to be actively developing a project for it to be useful - as long as a project has enough tests to make it safe to merge pull requests that pass continuous integration you can stay up to date on security updates and similar quite easily.
We built Doppins (https://doppins.com) to be able to use pinned PyPI dependencies and/or ranges and still keep them up-to-date continuously. Still another tool, but it's quite quick to enable on a repository and doesn't require any maintenance afterwards.
Creating a Lisp is a great way to learn a language. https://github.com/kanaka/mal/ has thorough tests and step by step instructions to help you along the way, definitely recommend checking it out.