There are fresh mangos in 36 / 6 = <<36/6=6>>6 dishes.
Thus, there are 3 + 6 + 1 = <<3+6+1=10>>10 dishes with mango on the buffet.
Oliver can pick the mango out of 2 of the dishes, so there are 10 - 2 = <<10-2=8>>8 dishes he won't eat.
Thus, there are 36 - 8 = <<36-8=28>>28 dishes left for Oliver on the buffet.
#### 28