DIY Router sled Kit. 20mm linear bearings rails and supports – United Clamps
Mssoomm Linear Rail Shaft Guide and Linear Bearing Slide Block, 2Pcs SBR12-5.91 inch / 150mm Rails +4Pcs SBR12UU Blocks with End Stops to Choose for CNC Router Machine and 3D Printer: Amazon.com:
Linear bearings | Router Forums
How to Flatten Wood with Linear Rail Router Sled - YouTube