Found: A.S.Solutions Flat Mount Adapters for Post Mount and IS frames and forks - Bikerumor
Adapter for Flat Mount Caliper on 140 mm Post Mount - A.S. Solutions
Shimano Flat Mount 160 mm To Flat Mount 180 mm Disc Brake Caliper Adapter, Black | Bikeinn
Front Flat Mount Disc Adapters – Paul Component Engineering
Amazon.com: SwishTi Cyclocross Gravel E-Bike Bicycle Bike Flat-Mount Disc Brake Adapter for Flat-Mount Forks and Post-Mount Calipers use w/2pcs FM Bolts : Sports & Outdoors
Problem: Flat Mount Brake Calipers On IS Mount Frame | VeloNut
Bicycle Flat Mount Disc Brake Adapter Front 140mm 160mm FM Calliper For-SHIMANO | eBay
Shimano Flat Mount Caliper Adapter 140mm to 160mm Disc Fitting Guide - YouTube
Wolf Tooth Post to Flat Mount adapter puts new brakes on old frames, forks - Bikerumor