Used Car lot, will have some from time to time, but be prepared to wait for it. Otherwise, if you complete the IA licences, with at least bronze, you get a truck that way too.
hey which one?
Just do the IA test to get the Dodge or keep an eye out in the used car dealer. I have saw the F150 Lightning at least 3-4 times so far. I have 3 trucks right now. Dodge from the test, F150 modded for racing and the Toyota which I just got because it was there****, I'll finish all the events except the truck one and then look for someone willing to trade.
I've got a Dodge Ram Laramie, mildly modded that I used to complete this race. You're welcome to borrow that if you wish.