A quick Google search turns up the following three sites:
Emachines T6412 Motherboard Replacement (Includes CPU and CPU Fan)
$109.95 new - Cputopia.com
Emachine Parts - mbem104571ms : eMachines Motherboard (System ...
$445.00 refurbished - Impact Computers ...
Emachines T6524 T6522 T6412 Motherboard Ms-7184
$45.00 used - eBay
Google is your friend! Use it.
I would go $45 for a replacement motherboard, maybe $109 if I had very important stuff on this computer but $445 would buy a budget system that is many times faster than your old socket 939.