C# - can't find my winforms control in WPF toolbox

I made custom winforms control from one project, then I switched to WPF. I referenced the old project, but my custom controls doesn't show up in toolbox, and there seems no "easy" way to add them to my winforms host. Do I have to add them in code?

Also, if i decide just to re-write the codes in wpf, how difficult/different would it be?