This would be accomplished the same way that you would add any custom control to your toolbox.

Rightclick on the grey area of your toolbox.
Select Add/Remove Items...
Sort the display by namespace
Look for Oakleaf.MM.Main.Windows.Forms.Infragistics
Place a checkmark next to the controls you want
Click OK

That should do it. I did mine a bit different but the idea should be the same.