I sent my message below at the end of December, but never heard anything back. I realize that the end of December was bad timing; many people were likely to be away for year-end holidays. Thus, I am following up.
The boards I have, in rough order of ascending age, are:
* MSI MS-7548 v1 (Compaq Aspen GL8E)
* MSI MS-7310 v1 / K9N4 Ultra-F
* Asus M2N-SLI Deluxe
* Supermicro PDSME+ v1.1
* Jetway VM2DMP v2
* MSI MS-6119 v1.1 BX2
(There's a couple others in storage I can dig out if there's interest, an Asus A8N or A8V, and something more recent, IIRC)
I realize that some of these are rather old, but there are similarly old motherboards listed in the supported motherboards list on the wiki, so I hope I'm not offering obsolete junk that Coreboot has no interest in, or has decided not to support any more.