Applescript: insert string in filter or check item in list

Question

Friends and experts:
I'm trying to get my script to check for particular system voice and if it not found, to prompt the user to install it before the main body of the script runs.
From everything I've read, it seems that I'm going to have to do this via GUI scripting (but if anyone can offer a better alternative I'd love to hear it - the GUI script is clumsy and not to my liking. Anyway...)
I've cobbled together a clumsy GUI script to do all but the last part - how to check the item I want, or alternatively have a string placed in the filter bar so that only that item will be shown to the user. This is the UI element I'm wrestling with:
And this is the portion of the script that deals with open sys prefs, selecting the system voice button and bringing up the 'Customize...' menu.
openSys()
delay 0.5
openVoice()
on openSys()
          tell application "System Preferences"
  activate
                    set current pane to pane "com.apple.preference.speech"
                    reveal anchor "TTS" of current pane
          end tell
end openSys
on openVoice()
          tell application "System Events"
                    tell process "System Preferences"
                              click pop up button 1 of tab group 1 of window "Dictation & Speech"
                              click menu item "Customize..." of menu of pop up button 1 of tab group 1 of window "Dictation & Speech"
                    end tell
          end tell
end openVoice
Can anyone help me solve the last piece of the jigsaw? Suppose, for example, I want 'Alva'. How do I check that or add 'Alva' to the filter bar?

Answer 1

Thanks for the tips, Frank & red_menace.
Actually, getting the available voices isn't the issue. The script relies on one particular foreign language voice, and the easiest way to test for that is just to start the script with an empty 'say' command using the required voice:
say "" using voice "Narisa"
If "Narisa" isn't installed, it'll throw error code -244, so I can catch that and prompt the install. If it is installed, the script simply moves on to the next line of code.
Ironically, I'd only got into AppleScript in recent months after realising I could do certain things much easier than with Bash or struggling with Cocoa, which I'm still very much a novice at. However, I think what I've learned here is that it's a case of using the right tool for the job. Since AS seems unable to pull off what I want to do, I'll put this on hold and go back to learning Obj C, Cocoa and XCode.
Although I didn't get the answer I wanted (a way to do it with AS), I think the answer is that I need to move this project to XCode, utlize the Applescript that I've got and add the required Cocoa classes as necessary.
Thanks again both for your input. Lesson learned!