I usually only use the numberic pad when I need to fill an excel sheet or something of that sort. If you encounter some numbers in a normal text, try using the row on the top of your keyboard... It's way faster since you don't have to search the number-pad homerow key, and you'll get the hang of it pretty quickly if you can touch-type normal letters.
As for keypad training... I don't really know a site for this. Maybe grab a phone book and type random people's phonenumbers down?