To the best of my knowledge, Digiland, the Walmart/Onn affiliate that manufactures these tablets, has yet to release any kernel source. However, kernel source isn't required for a LineageOS port ROM. Since most of these tablets are Project Treble supported, there are probably existing GSI custom builds that will boot up and run on the Surf 7 (100005206). I am now finishing a custom ROM on a Lenovo Tab3, and the 100005206 will be my next project for a custom ROM once I finish up. I can post my progress here to keep any interested members informed.