Here are some updates in Dec 2020.
I have some Let’s Split v2 PCBs (designed by /u/wootpatoot) for sale. It’s one of the most popular DIY split, ortholinear mechanical keyboards.
This post contains some of the pro micro alternatives.
The Let’s Split v2 guide uses the CP-43514-ND TRRS jacks, which can be sourced from Digi-Key. The shipping fee can be high outside of the US. An alternative is to use a 7-pin PJ-362. They can be...