As far as I understand you have to register your command into the right component category:
private static void Reg(string regKey)
private static void Unreg(string regKey)
Not sure if there exists an appropriate component category in your case, but you may have a look into the ESRI.ArcGIS.ADF.CATIDs namespace, there are a lot of component categories listed. Maybe there's one for the attribute table also...
Thanks for your reply. But for placing command in specific place (such as toolbar) a developer should use ICommandBars.Find method to find appropriate toolbar or context menu. In order to call this method the identifier (CLSID or ProgID) of the toolbar has to be known. This IDs are published in the ArcMap Ids article, but I cannot find the one for attribute table window toolbar there.