These Saw Horse Shoes are 3D-printed out of PETG plastic.  I created the CAD design myself from the remains of a broken, original shoe.  PETG is an ideal plastic for this application.  It is minimally impacted by UV exposure and its glass transition point is ~85C.  This means that its structural strength remains sound until its temperature exceeds this value (185degrees F).

I am now using these replacement shoes on my own saw horses, as I was unable to get shoe replacements from Harbor Freight (see images for BLACK plastic shoes installed).

I anticipate that I am not alone with the cracking OEM shoes on my saw horses, so I am making this option available to others.  This will avoid the direct steel-to-concrete/dirt alternative once your shoes crack and fall off.