Here’s a little addon that adds a Select Clone Object Master command to the viewport context menu for 3d objects.

The addon is a single self-installed plugin that includes a command, a menu, and a filter:

• The menu item calls the command.
• The filter controls whether or not the menu item is enabled…so that the Select Clone Object Master command is enabled only when you ALT+right click a clone.

# SelectCloneMasterObjectPlugin
# Initial code generated by Softimage SDK Wizard
# Executed Thu Jun 7 10:55:31 EDT 2012 by blairs
# 
# Tip: To add a command to this plug-in, right-click in the 
# script editor and choose Tools > Add Command.
import win32com.client
from win32com.client import constants

null = None
false = 0
true = 1

def XSILoadPlugin( in_reg ):
	in_reg.Author = "blairs"
	in_reg.Name = "SelectCloneMasterObjectPlugin"
	in_reg.Major = 1
	in_reg.Minor = 0

	in_reg.RegisterCommand("SelectCloneMasterObject","SelectCloneMasterObject")
	in_reg.RegisterFilter("Clone",constants.siFilter3DObject)
	in_reg.RegisterMenu(constants.siMenu3DViewObjectSelectContextID,"SelectCloneMasterObject_Menu",false,false)
	#RegistrationInsertionPoint - do not remove this line

	return true

def XSIUnloadPlugin( in_reg ):
	strPluginName = in_reg.Name
	Application.LogMessage(str(strPluginName) + str(" has been unloaded."),constants.siVerbose)
	return true


# Match callback for the CloneFilter custom filter.
def Clone_Match( in_ctxt ):
	Application.LogMessage("Clone_Match called",constants.siVerbose)
	o = in_ctxt.GetAttribute( "Input" )
	c = win32com.client.Dispatch( "XSI.Collection" )
	c.Items = '%s.%s' % (o.ActivePrimitive.FullName, 'CopyOp')
	return c.Count > 0
# 	Return value indicates if the input object matches the filter criterias.


def SelectCloneMasterObject_Init( in_ctxt ):
	oCmd = in_ctxt.Source
	oCmd.Description = ""
	oCmd.ReturnValue = true

	oArgs = oCmd.Arguments
#	oArgs.AddWithHandler("Arg0","Collection")
	oArgs.AddWithHandler("Arg1","SingleObj")
	return true

def SelectCloneMasterObject_Execute( Arg1 ):

	Application.LogMessage("SelectCloneMasterObject_Execute called",constants.siVerbose)
	Application.Selection.Clear()

# by Vladimir Jankijevic
# https://groups.google.com/forum/?fromgroups#!searchin/xsi_list/Finding$20the$20source$20mesh$20of$20a$20clone/xsi_list/cyUYARDMooA/J3JVxc6jJtIJ
	copyop = Arg1.ActivePrimitive.ConstructionHistory[0]
	Application.Selection.Add(copyop.InputPorts[0].Target2.Parent3DObject)

	# 
	# TODO: Put your command implementation here.
	# 
	return true

def SelectCloneMasterObject_Menu_Init( in_ctxt ):
	oMenu = in_ctxt.Source
	oMenu.AddCommandItem("Select Clone Master Object","SelectCloneMasterObject")
	oMenu.Filter = "Clone"
	return true