Hi Paul,
Sprag part numbers for various makers are:-
Renold Part. No. REGP 4972 (4C)
Borg-Warner Part.No. BWX 1310003
Formspragg-Steiber Part. No. DC 4972 (4C)
Ringspann Part. No. 3677.049.602.000000
They should be available from the major Bearing Stockists or Engineering Suppliers.
I bought a batch from Eriks 10 years ago but have sold/used them all.
Jeff had a batch on this forum in 2015 and sold them all.
Not sure which companies are open for orders during the current crisis, so if you need one urgently, Peter & Claire White should have them in stock and Rob Bennett often has a stock of them in his spares supplies.
Hope that helps.
Dave H