Re: I just ordered a custom built HP laptop...
Any HP retailer who sells business products (Elitebooks, Elitedesks etc) should be able to order a custom computer with Freedos. Similarly Lenovo also offers some models with Freedos. Dell did, don't know if they do it anymore.
Do note that if you buy a computer with Windows 10 Pro license you're still eligible to downgrade to Windows 7 pro.