But nowadays, blogspot do not put it as priority at their top gadgets. So new blogger does not have it.
To grab it, follow the step given in the picture bellow (click to enlarge)
1. Click Layout and Click Add a Gadget
2. Click More Gadgets
3. Scroll down and find the FOLLOWERS gadget. If you cannot find it, click next>> until you encounter it.
Ok that's all. Enjoy ^_^