Check the LPC ROM controller on your board--it'll probably be a Winbond chip. They are often capable of using a wide variety of chips, and your motherboard itself couldn't care less so long as the controller works with the chip. They're all very similar. If so, you could try a more generic ROM of the capacity you need. You might also try padding your image with zeros to match the capacity of the ROM. I'm not sure if you need to pad the beginning or end, however. I had a chip fail some blocks near the end and the 8KB boot block was surprisingly dead. Could have just been a glitch.