Is there any time frame from which you purchase a vehicle that you can or can not request a Carfax report .

There's no legal obligation to give you a Carfax if that's what you're asking. Two and a half months out from vehicle purchase you are pretty much on your own I assume this would hold true with any dealership

I agree, but failed to ask for it at the time of purchase, I have owned the vehicle for 2 1/2 months and have asked for a Carfax from the dealership and they tell me they can't, because I've already bought the vehicle, does anyone know if this is true.

Usually you get that before you buy the vehicle