A flat mount disc caliper on a post mount frame? There's an adapter for that - CyclingTips
Flat mount forks and frames for 140 mm disc brake rotor | SHIMANO BIKE-US
Wolf Tooth Post to Flat Mount adapter puts new brakes on old frames, forks - Bikerumor
Problem: Flat Mount Brake Calipers On IS Mount Frame | VeloNut
Found: A.S.Solutions Flat Mount Adapters for Post Mount and IS frames and forks - Bikerumor
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
Add Flat Mount Brakes to Post Mount Frames and Forks with Our New Post – Wolf Tooth Components
Direct mount to flat mount adapter Kinning Cycles - YouTube
Road Disc Brake Tech: Flat-mount vs Post-mount - Bike Hugger
Shimano Flat Mount 160 mm To Flat Mount 180 mm Disc Brake Caliper Adapter, Black | Bikeinn
Flat Mount to Post Mount Brake Adapter for 160mm Rotor | eBay
Amazon.com : SHIMANO Flat Mount Disc Brake Adapter Front, Flat Caliper to Flat Mount, 140/160mm : Sports & Outdoors