Lightening Connector

Lightning parts aren’t going to be readily available, short (no pun intended) of harvesting your own.

Pin headers are fairly typical for directly connecting together two boards, but I’m guessing you want some distance and a cable?

Mouser has zillions of connector choices.

As for alternatives to Lightning, keyed 8P8C RJ45 connectors, or 10P10C, maybe. Or scrounge some DEC MMJ connectors. DIN. Lots of options. Might even be able to re-purpose USB-C to add your own protocol, though that’ll be more work to implement.

I did see this on Wikipedia:

"Apple is the sole proprietor of the trademark and copyrights for the designs and specifications of the Lightning connector."

Since it is proprietary, you probably won't be able to find it at Digikey. The male would be no problem, the female is what will be impossible.

I imagine these would be expensive. I like the Molex microfit

https://www.molex.com/molex/products/family/microfit_30

(It might be easier to find if you spell it correctly: Lightning)