You could add the thread you're interested in to the Bookmarks stored in your browser. That way you can go to the thread regardless of who you have ignored.
The MR website has a particular form of URL that will take you to the first unread post in a thread (if there is one):
Code:
https://forums.macrumors.com/threads/blocking-users.2403237/unread
If your browser allows you to manually edit the URL of a Bookmark, you can edit your saved bookmark so it looks like the above. Obviously, the part before "/unread" should refer to the thread you want to bookmark.
EDIT
Here's another way I just confirmed.
1. Go to the thread you're interested in and click the "Watch" button at the upper right of any page in the thread. Confirm it.
2. Go to a post by the user you want to ignore. Hover over the avatar. Click "Ignore".
3. Refresh the page. Confirm that the user you just ignored doesn't appear.
4. Under "Watched" in the Home/New Posts/Watched bar you'll probably see a red-boxed number for the count of watched threads that have new posts (assuming the watched thread is very active). Click it.
5. Your list of watched threads should appear. Notice that the thread you chose to Watch DOES NOT appear in the list. This is because you're ignoring the user who started the thread.
6. Look at the lower right of the list for "Show ignored content". Click it.
7. Observe that the watched thread started by the ignored user now appears.
8. Click the thread and it should take you to the first unread post in the thread.
This works because when you're ignoring someone, almost every page that would otherwise show content by that user will instead show a "Show ignored content" link somewhere on the page.
I haven't confirmed this on every possible page, but I've seen it enough times in different contexts that I thought checking for it in the Watched list was worth doing. When I did, I saw it and knew that Watching a thread could work even for ignored users.