Is there any way to install gui on ubuntu server 12.04 in offline using any packages. Is there any deb package available for install gui.
No, if you want a GUI, then you should use the desktop install medium. There's no difference between Ubuntu Server and Ubuntu Desktop except the default packages. That is, you can install all services on Ubuntu Desktop as well.
You could download a Ubuntu 12.04 DVD image1 and assign that as one of the package sources. Based on this answer to another question (edited quote):
The last part in one command that is
and install the regular GUI:
(The caret is not a typo, it is used for APT tasks.)
And it's always a good idea to check for the latest point release of an LTS version. At the time of writing 12.04.2 is available as ISO CDROM and DVD images. You could use the CDROM, but the DVD contains a lot more packages.
1 Yes, DVD, not CDROM. Those images are not mirrored to all mirrors, so be careful in that. The main mirror lists them: http://cdimage.ubuntu.com/releases/12.04/release/