I think Bachmann spectrum had a DD40x out a couple of years ago.
Actually U.P. didn't build them. EMD came out with the DD35 first to see if anyone was interested. U.P. was always looking for big power to pull Sherman Hill and other grades on the railroad. When they ordered the loco's EMD had started building the gp40, so they got DD40x instead. The S.P. had three dd35 cabless b units. I'm not sure if U.P. got dd35s or if all of their units were dd40x's. Basically the model numbers tell the whole story. A "b" truck is 2 axles. A "c" truck is 3 axles, so a "d" truck is four axles powered. The dd35 was 2 gp35 prime movers on a common frame with 2 "d" trucks hence dd35. The dd40x was the same thing with the prime movers of 2 gp40s on a common frame. The "x" in the model designation stood for experimental. Rail fans used to call them 6000 hp track straighteners. The U.P. has a pair of e units, the dd40x, the challenger, & the fef northern in their historic fleet. A few years ago before the S.P. merger the U.P. was facing a severe power shortage. If I remember correctly, the fef was being overhauled, but the challenger, the dd40, & the e units were all used in revenue service in the midwest to help meet the need. Also when ever the U.P. shops one of the historic fleet units, when it comes out of the shop and needs to be tested with a load, they will put it in front of a revenue service train, so a modeler wanting to run a dd40x or a challenger in front of a train load of double stacks is not out of line at all.