I have attached the parts pricing/list. This can be found on the support section of the HES webpage. I suggest you note down the part numbers you need, then either call the Austin office or your Regional Manager. If you tell me where you are, I can tell you who to contact.
Just to add to this, it would be beneficial for you to call the HES service dept before you order a board as they can tell you if it is actually broken or not aswell as make sure you get the right model.
*I do not work for HES, this is just what I do when I need a part*
Officially, the only supported motherboards are the 5 kinds of boards supplied by HES with the HES custom BIOS. These are the configurations that the test, and support.
You *might* be able to get some other motherboard to work, but it's unlikely. The iPC OS image only has drivers for specific hardware.