Why moodle 2.2.3 is discontinued and is not available on moodle.org site. Please let know about the same. Request you all to treat this as urgent.
This should not come as a surprise to you. Support lifetimes for all Moodle releases are given on http://docs.moodle.org/dev/Releases, and have been there since 2.2 was released.
Anyway, it is not discontinued. It is now recieving reduced support (security fixes only) until June. Even after that, it will be unsupported, but no one is going to take it away from you. It just won't receive any more fixes of any sort.
sumit sh "Request you all to treat this as urgent."
Well, this matter may be urgent to you, it's not urgent to us. It is useless and unproductive to post "urgent" messages in forums in general. Cf. How To Ask Questions The Smart Way.