Found it on both the standard numeric palette and on my express palette (has an icon depicting two yellow cubes):
Functions -> Numeric -> Scaling and mapping
Functions->Express->Arithmetic and comparison->Scaling and mapping (the path may vary depending on the palette setup...).
However if you can't find it try searching for it. Click the search button on top of the functions palette and search for the VI.
Could be that it only comes with some of the development systems, we've got the full developer suite, if you only have the basic e.g. it might not be included (?).