Sadly, nearly all the manual/multipart files on Uloz for Harmy’s Despecialized Editions are dead. Checking Harmy’s posts (click on a user’s name to see their post history) reveals that he was searching for a replacement host in May & June, but I do not think he has uploaded the files to a new site yet.
The mkv files you have found on Uloz look suspicious/unofficial to me; I suspect they are re-encoded and heavily compressed.
Fortunately, some kind soul appears to have uploaded the most recent mkv files for all three films on Usenet within the last year. Search for “despecialized” on NZBKing. If you haven’t used Usenet before, I recommend getting a free account from the “free-usenet” provider along with NZBGet software (also free).
JEDIT: See this guide to Usenet.