How could Uchiha Madara suddently use a new Jutsu he never used before? Well, I'm talking about the Senpo: Inton Raiha and the Senpo: Ranton Kouga.
To perform these two jutsus, one must have the Sage of the Six Paths senjutsu.
These are not common jutsus and I don't believe Madara has ever saw someone using them.
At first I would like to quote this from wiki:

Intelligence of Madara Uchiha


  Madara's years of experience on the battlefield honed his strategic
  ingenuity. He could quickly devise a number of approaches and could
  switch approaches immediately. He could form and verify any theories
  he comes up with using small details. In addition to his sheer
  adaptability, Madara was knowledgeable on a large variety of individuals and abilities, and thus could identify techniques when used and react with the most appropriate counter to them.


Means he was knowledgeable and he was having so much of knowledge that he can perform various types of technique by simply observing them. There is no doubt that he was one of the kind with such a great observation skills. 

There also one point which is worth noticing that :


  Madara do not use certain techniques more than once


Also you may think that performing those technique it take more than 1 year of practice before it can be use in real fight. But Madara has large chakra reserves which allowed him to fight nonstop for twenty-four hours before collapsing. He was skilled in chakra control as he could perform complicated techniques with a single hand seal. This is partly because he inherited Indra's chakra.

This point is also worth noticing which explains a little about how he can perform various technique :


  He is able to identify people and their powers by sensing their chakra
  and masters the mightiest fire-based attacks in existence:
  overwhelming streams of fire, gigantic clouds of searing ashes, and
  powerful fireballs shaped like dragon heads, just to name a few


There are few more possible explanation which proves that Madara has some real observation skills :



  When Madara awakened his Sharingan as a child, with one tomoe in both
  eyes. With brief eye contact, Madara could place targets under
  genjutsu and paralyse them or relay information.



So while fighting he used to gather enough information about the technique which his opponent uses. You must also note that Madara was in so many fights so just think how much experience he is having. 



  Madara and his brother Izuna were the first Uchiha to awaken the
  Mangekyō Sharingan. Madara knew about other users Mangekyō
  techniques, and was also capable of discerning the mechanics of these
  techniques with brief observation.



So he was able to learn all those techniques with brief observation.



  Madara Uchiha noted that the Sharingan can only be used to its full
  potential when both eyes are together.



This proves that he observe everything carefully.

After noticing all these points there is no doubt that Madara got some serious observation skills and also he always try to use new techniques every time. It might be true that he may have never known about few Jutsu and also he have never used it or seen it anywhere but he may have observed it and may have learned about that new Jutsu before he have tried it.



Source - 

http://naruto.wikia.com/wiki/Madara_Uchiha

http://naruto.wikia.com/wiki/Rinnegan

http://villains.wikia.com/wiki/Madara_Uchiha