Building a Bicycle Trailer

Does anybody know where can I buy a bicycle trailer axle kit like

How to build a DIY trailer for a bicycle or e-bike!

18 DIY Bike Trailer Ideas For Single Bikes - DIYnCrafty

Mark Rehder - Bicycle Utility Trailer

How to make a cargo trailer? - Bicycles Stack Exchange

How to Build a Bike Trailer - Instructables

Building Bamboo Bicycle Trailers

The best DIY bike trailer instructions - reacha

How To Build A 1000$ Bicycle Trailer For $450

DIY Budget Bike Trailer

Solar-powered electric bike camper includes bedroom and dinette

My Home-Made Bike Trailer – The Ottawa Cyclist

Electrically Powered Bicycle Trailer & Hand Cart (DIY)