Amazon.com : CyclingDeal Bicycle Shoes Cleats Adapters - for MTB Shoes to Use with Cleats of Road Bike Pedals - Compatible with Shimano SPD-SL, Look KEO & Look Delta - Converting Adapters
Tutorial - How to switch from 3 holes to SPD - YouTube
Bontrager Road Shoe SPD Pedal Adapter | Trek Bikes (INE)