There may be some misunderstandings on Unicode and fonts and Unicode fonts which cause the question, and makes the answer more difficult than you would expect:
From the Unicode website:
The Unicode Standard is a character coding system designed to support the worldwide interchange, processing, and display of the written texts of the diverse languages and technical disciplines of the modern world.
Fonts that “support Unicode” promise to the operating system or to the application that uses them that they provide an accurate graphical representation (glyph) of the code points they implement. A “Unicode font” typically does not cover each and every Unicode code point, but rather only subsets of the standard (Unicode Blocks).
Typically it is the operating system’s responsibility to find a matching font when displaying Unicode text.
So how can you find a free Unicode font supporting most of the characters? Here’s a list of links:
- Hanazono (52,809 CJK characters, full Ext A, Ext C, partial Ext B)
- GNU Unifont Glyphs (BMP 5.1)
- Unicode Font Guide
- Alan Wood’s Unicode Resources (fonts by range)
- Gallery of Unicode Fonts