Same issue here... Found them on another disk though... iTunes will just say the files are missing and wil not process them. They'll be marked with an exclamation mark in front of the track name when in the numbers view. I first had to re-link the files (thus iTunes copying them to my iTunes Music folder) and then had to run iTunes Match again.
Sorry, iguess no workaround here. I may dsuggest you find a copy somewhere and then re-download them from the cloud.