How many times has the original Nine Tails attack been flashed back?
In the anime series? Who knows.

But in the manga:

Naruto chapter 1, page 1, 17, 37, 49
Naruto chapter 2, pages 13-14
Naruto chapter 2, page 5    
Naruto chapter 2, pages 14-15
Naruto chapter 500, pages 8-9
Naruto chapter 500, pages 9-10, 12
Naruto chapter 607, pages 6-7
Naruto chapter 500, pages 13-17
Naruto chapter 501, pages 1-6
Naruto chapter 501, page 7
Naruto chapter 501, pages 12-17
Naruto chapter 502, pages 1-6
Naruto chapter 502, pages 7-17
Naruto chapter 503, pages 3-4, 8
Naruto chapter 503, pages 5-7
Naruto chapter 503, page 9
Naruto chapter 503, pages 10-17
Naruto chapter 503, pages 13-19
Naruto chapter 504, pages 1-9
Naruto chapter 504, pages 10-14
Naruto chapter 440, page 15
Naruto chapter 499, page 3
Naruto chapter 440, page 5
Naruto chapter 399, page 15
Naruto chapters 399-401
Naruto chapter 484, pages 8-9
Naruto chapter 485, page 6
Naruto chapter 399, page 16
Naruto chapter 502, page 2


Naruto: Shippūden episode 68

Naruto chapter 149, page 9
Naruto chapter 370, pages 15-16
Naruto chapter 386, page 11
Naruto chapter 399, pages 14-15
Naruto chapter 440, page 10
Naruto chapter 500, page 7
Naruto chapter 597, pages 20-21