Grumble Grumble Grumble
There are 49 episodes listed for Getbackers. (TBS Japanese Website http://www.tbs.co.jp/getbackers/ ) with no announced plans for spinoffs, OVAs, or additional productions...
ADV Films has the US Region 1 distribution rights, with the 4th DVD (of which I'm collecting) recently released. (I haven't seen the FanSubs, so NO SPOILERS!!! grumble grumble grumble..)
ADV Films GetBackers Splash Page