Hello Everyone,
You can find the clamp at Grainger's. They are called motion control couplers and they are manufacture by Ruland Manufacturing.
RULAND MANUFACTURING
1 Piece Clamp 1/2" x 3/8" Bore Dia. 1215 Lead Free Steel Rigid Shaft Coupling
Item # 2AMF7
Mfr. Model # CLX-8-6-F