I will attempt to get the Non ABO Rh antigen units (C-0.2, K-0.91, Fya- 0.34, Jkb- 0.28) C*K*Fya*Jkb gives 0.0173 which gives number of units to be screened as 1/0.0173 or 57.8 or roughly 59-60 units to get ONE antigen negative RBC unit.
If you want to consider the ABO Rh then O Rh Neg is 0.40*.15 or 0.06. multiply this with the former will give 1/0.00104 or 964 units!! scary. good luck