Gluck has published an unoffical forms package which from a fork of ReactiveUI repo:
Note that reactiveui-*-events packages (neither the ones from Anaïs, nor Gluck's) have no adherence to ReactiveUI per-se, you can do RxUI without them, and you can use them without RxUI. They're simply "generated extension methods for every type exposing .Net events to expose corresponding IObservable wrappers", to save you the burden of writing the FromEvent/FromEventPattern yourself.
This winforms package contains helpers for every type in System.Windows.Forms.dll.