The Let’s Split v2 guide uses the CP-43514-ND (SJ-43514) 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 (PJ-362A). They can be found on eBay.
The 3 extra pins of the PJ-362 can be extracted by a nipper.