Why is there repetition of the measure words in 一把把小扇子 and 一枚枚邮票?
There is a similar question What does the second &quot;幅” mean in the following sentence?

My answer there should be applicable here too.


  "一幅幅" in "一幅幅美丽的山水画" mainly means 'one after another'


With the same logic,  一把把小扇子 and 一枚枚邮票 means "one small fan after another" and "one stamp after another" (meaning many fans and many stamps)