Rev. Nat's cider has a lacto sour cider, the website says he has "unlocked" the secret of using lacto in cider:
http://reverendnatshardcider.com/ciders/sacrilege-sour-cherry/
I can't get this cider where I'm located, but would like to try it.
When the sour cherries are ready in the orchards here I'm going to add 1 lb/gallon to some already fermented cider I have.
I'm thinking Rev. Nat is adding the lacto before regular fermentation, like you would "kettle sour" beer. Maybe even holding the apple juice w/lacto at 100F for a few days to help the lacto growth?
He's most likely using cherry concentrate and adding sugar to get the ABV to 7.6%?
Which lacto strain is best to use?
There's a thread on reddit where someone used brett brux from Wyeast in treetop apple juice &
another threat from HBT where a recipe and method is described that looks good:
https://www.homebrewtalk.com/showthread.php?p=6916408
Cigar city cider and mead has a sour cider and the madfermentaionist has a blog entry I haven't gotten to yet, so there's a lot of info out there. Good Luck !