Where is the WPF Numeric UpDown control?

Simply use the IntegerUpDown control in the Extended.Wpf.Toolkit
You can use it like this:

1. Add to your XAML the following namespace:

   xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"

2. In your XAML where you want the control use:

   <xctk:IntegerUpDown Name="myUpDownControl" />