You don't really need the chart in the toolbox to use it. When you drag and drop the control from the toolbox onto your form then all it does is generate a private field of the chart type and then create an instance of it in the *.designer.cs file and sets the properties. If you look at the contents of that file you can see the pattern it uses. So
1) Create a private field for the Chart.
2) In InitializeComponent
method create an instance of it
3) At a minimum set the Name
property to match the field name and set the initial size.
4) If it implements ISupportInitialize
(??) then call BeginInit
and EndInit
methods like it does for the other controls.
5) Add the control to the form's Controls
property like it does for the other controls.
You can now switch back to the designer and see the control and set properties normally. However, none of the custom chart editors will be available. Therefore anything you cannot directly set in the Properties window will have to be set by hand.
The recommended alternative is to create a dummy Winforms .NET Framework app. Add a link to your existing form in the other project. Then use the .NET Framework designer to edit the control. This is the hack approach for controls that don't support the .NET Core designer.