My question is simple, apart from the three themes pre-installed in Tkinter are there any other themes I can get ? Something like 3rd party themes ? If not, how can I change the button or other widgets looks (manually changing the form,etc..)?
Also I would like to know if it is possible to change the outside window look, like the look of the 

[ _ ] [ [] ] [X] 

buttons of the window, if not is there a way to remove them so I can put my own buttons in the frame?
Any code example or link is welcome.
You cannot change the window border, but you can remove it entirely and draw your own border. You'll also be responsible for adding the ability to move and resize the window. Search this site for "overrideredirect" for lots of questions and answers related to this feature.
As for third party themes: no, there aren't any.
3rd party Tkinter themes and modifying outside window buttons