It would be a downhill fork for downhill racing. If you want a bi-plane fork a lot of custom builders can make one so go for it. I probably wouldn't recommend something random built by who knows from some online sellers on some platform but Champman cycles comes to mind pretty quick for that but I know there are others. Maybe Crust did something as well I cannot fully recall at this point but I know they exist and have seen builders advertise their forks.