I just finished all the game, but the most rare Ones are impossible to get(the tower) Why? Can I do something about this? Thank you
They are purposefully uncatchable. You cannot catch them whatsoever.
Casi don’t worry all arks in the tower you can catch somewhere else in the world except the boss arks. There might be very few you can’t but almost all of them you can. You just have to look in the right spot. If there is a ark your looking for maybe I can point you in the right direction. 
The arks in the Tower are meant to be uncatchable, just the way the game made it. In the story it tells us that we are the only hunter strong enough to even enter the tower, yet we are not strong enough to catch the arks within because they are just that strong.
All right, Thanks every one, I will be interested to know where can I find voltiger
He has 2 pre evolutions , u can Find voltyke the first one in the wild
Where exactly?
Im sorry I dont know , I got voltiger off a golden egg
Voltyke is the first stage of voltiger. He is found one step east of maldan. Be sure to keep looking as he is a bit rare so he might take a while.
If you need another ark I might be able to help.
Or check lachzeers thread
Third try and I found it, Thank you!! Can you tell me the one that looks like a dinosour and is a fire arkadion?
Vulcaraptor?
Yes!!!
If it’s vulcaraptor. The first stage is lavaraptor and is found 3 steps east of finam. If you have anymore questions look them up in the “Where’s that monster thread”
There is also a good site that I look on a lot, which may help you.
http://hunterisland.wikia.com/wiki/Arkadion_List
It has the list of all of the Arkadions, and most of them have where they are found (some even have pictures! :O)
Those 2 arkadions you’re looking for are both very very good once fully evolved! You won’t be dissapointed 
As someone above posted, the wiki page is an awesome resource, however it is painfully slow to load on phone. Shameless (hopefully) plug for the PDF I made:
http://www.hunterislandforum.com/index.php/topic/1304-pdf-moster-list/#entry21156
Also, you should get adobe Acrobat for the phone/iPod/iPad so you can access the list even when you lack an internet connection!