Hi Jmcbj4,
Make sure your WinMX is set to Auto Find Sources > 10mins Settings > Search > Default Download Parameters > AFS - remember previous or may say Auto Find Sources - 15 mins. Change this by clicking on it and choosing 10mins
Then on the Auto Enter Que or .. AEQ - Remember Previous... set this to 100. This will help insure you get in the que (in line) for the files.
Are you seeing these files red in the transfers screen? If so right click the file and set them to the above settings also. Then right click and choose 'Fine Alternatives' This should open a search window and then fine users that have an exact match to your file. Does it find any sources this way?
If not it may be that the files you seek are rare ones. Let us know what you find with the above settings changes and the search method please.