There were 3 engines that were put into these first generation trucks. The two smaller engines were both inline 6 cylinders, with the larger being a flathead V8. With a one-piece windshield and integrated headlights, these trucks looked much more like their modern counterparts than most other trucks being made at the time.
The three models that were sold as part of the first generation F-Series were the F-1 half ton, F-2 three quarter ton, and F-3 Heavy Duty.
You will have to search around to find one of these trucks for sale. You can go to shows and hope to find a restored one, but you'll save a lot of money buying one unrestored on somewhere like eBay. If you check out that site you might also want to look at the parts they have available.