If your range allows it, set up multiple targets at various distances apart.
And at various distances downrange.
Start with simple 8" circles, fairly close together and close to you.
As you improve, decrease the target size and increase the distances.
If you want to get fancy, buy a timer to let you know how fast you are.
It's hard to judge time otherwise.
If you want only bowling pin targets, like SgtLumpy said, just download a picture and print it out whatever size you want.
Google images, Ixquick images and others have plenty of them online.
Heck, bowling pins are real easy to draw freehand, too.