As Mystery indicated. The list can be ordered by newest post, most recent post, oldest post, etc.
Search the Suggestions forum using your search engine (i.e. Google or similar) with the following keywords: "site:http//lotrminecraftmod.wikia.com/wiki/Board:Suggestions_forum KEYWORDS".
Search the Community-Endorsed Suggestions Board using your search engine (i.e. Google or similar) with the following keywords: "site:http://lotrminecraftmod.wikia.com/wiki/Board:Community-endorsed_Suggestions KEYWORDS".
Search the entire wiki using your search engine (i.e. Google or similar) with the following keywords: "site:http://lotrminecraftmod.wikia.com/wiki KEYWORDS". This is more a lucky shot, in case the others didn't give any results and you're determine to find something.
Check the overview threads as listed here, and search using Ctrl-F "KEYWORD".
Do any form of manual search, in combination with the aforementioned options above.
Searching in a Board using Google is not very helpful. You can find out if there is a thread on that board with the keyword in the title but that's about it. The link that Google gives you also only leads to the board mainpage and not to the thread.
You could search for site:http://lotrminecraftmod.wikia.com/wiki/Thread to search through all threads, but that will also yield non-suggestion threads or other thread posts as results.