Sources for Trackball Units

[Tarzan]

Anyone have any recommendations for sourcing new/replacement trackballs?  I'm thinking of replacing the trackball in the military Marquardt keyboard, possibly with a steel ball unit to fit with the metal theme.

I'd been pointed to this company as a potential resource, anyone have experience buying from them?
http://www.ipc-systemes.com/pc/industriel/uk/Trackball+TouchPad-26.html#/liste.php?identifiantId=26&lang=uk&pmenu=

[insilica]

What size?

If you want metal you can always opt for ball bearings. The company you linked has nice offerings, but very expensive IMO.

E.g. here in UK: http://simplybearings.co.uk/shop/index.php?cPath=23

Alternatively ebay, like I said though depends on size. There are some nice sphere balls made of natural stone which can be had, just ensure it's perfectly spherical.

[Tarzan]

I probably should specify that I want to replace the entire trackball unit, preferably with something that has a USB cable already attached.  I don't have much info on the stock trackball on the Marquardt board, there is a reference on the DT wiki that says it can be made to work, but I don't have enough technical skills to follow the instructions.   

So I'm thinking of just replacing the whole stock rollerball assembly.  It's a square unit, about 55-58mm across, the actual ball itself is maybe 35mm in diameter.  No buttons on the stock unit, the keyboard uses three of the keys above the number pad for mouse buttons.

Anyone swapped a rollerball into a keyboard before?