Well as per your need, I would like to suggest to create a custom keyboard because the stock keyboard which comes with the device may not have the special characters you need.
You can refer the following tutorial to create a custom keyboard
http://www.fampennings.nl/maarten/android/09keyboard/index.htm
or you can see this search result which may serve your purpose,
https://github.com/search?q=android+custom+keyboard&ref=cmdform
And from below site you can get the list of Unicode characters which Android supports,
http://en.wikipedia.org/wiki/List_of_Unicode_characters
http://unicode-table.com/en/#0026
Note: Writing the whole code to create a custom keyboard is beyond the scope of this answer, so I mentioned the reference link.