I'm 5'11", 150 pounds.

On my bulking diet (about 3200 calories), what would be a reasonable amount of carbs for a day?

I know for protein I want 1.5-2 x Lean Body Mass, but what about carbs? Is 250 too many?

Well if your eating 1.2 - 1.5 grams of protein per pound of body weight, and your fat intake should be 20-30% of your total caloric intake, the remainder of your calories to achieve your target intake would come from carbs.

exactly what falco said. you know what your protein intake should be. you know that 25-30% of yoru total calories should come from fat (about 88g of fat is 25% calories of 3200)...so make up the remainder in carbs.

Typcial carbs for bulking is 2-3g per pound of lean bodyweight, so 250g sounds entirely reasonable, if not a little low.