spidermonkey...
www.videoconnect.com (or tion.com) was selling new ones a while ago... worth a look.
And try to save the control panel if you can. Something you might consider is having a mini-hotswappable control panel.. (there is a few examples... a really good one on a cocktail table).
Where you have on each side 2 areas that can come off/on. Each with enought space for a joystick and buttons... or 6 buttons.... or a trackball..
This way you can have 4 joysticks (left and right on each side with just a joystick)
Or your originals and some buttons.
Or a joystick and buttons.
Or a trackball and buttons
or a spinner and a flight stick...
It would tear up the original control panel.. but might be what you want.... building a non-flat control panel will be hard (if you want multiples)... so you might just take 2 bocks out of each...