Usually when you need something really specific like that and you're not selling this PC to someone else, it's best to just make your own. Get a c13 or c14 rewireable end, cut up an existing cable, and stick it on there. As long as you do a clean job and don't put the wrong wire on the wrong terminal and it's all secured properly you'll be fine.
If you cinch a small ziptie down really tight on the black insulation right where it tries to exit the end you modified, you can give it some extra strain relief and reduce stress on the terminal screws.