Good guys of LOTR clueless?

[Earendilyon]

Originally Posted by Maédhros

He could have done exactly the same thing that he did later on. Go to Minas Tirith and look for clues about the Ring that Isildur wore. Simple.
He didn't have to wait for 59 years to do it.
Twenty rings sounds "many" to me.

I do think 20 rings do not count as many, but that's not very important here. I assume Gandalf had more things to do than hunt for info on the ring Bilbo possessed. It probably was not the top priority on his list at first. Also, he probably didn't know where to exactly find the information he needed. Maybe he first went to Rivendell, then to Lórien and finally to Minas Tirith. We neither do know how large the archives were he had to search through. I assume they were after some 3000 years rather huge, and probably not as nicely inventoried as modern archives. Remember also that he didn't get easily access to Minas Tirith's archives of Denethor. All these things would have cost consideral time

It seems to me that you need to keep on reading the other paragraphs of The Disaster of the Gladden Fields

Isildur was slained in year 2 of TA. It is in 2463 when Déagol the Stoor finds the One Ring, and is murdered by Sméagol.
Then we find out that Saruman begins to search the Gladden Fields at 2851 TA.

If what you say is true, then both the Elves and Men who searched for the remains of Isildur must be very incompetent or clueless.
Look, Déagol found the Ring in 2463 TA, meaning that 2461 years had passed from the death of Isildur, and Saruman found items belonging to Isildur in 2851 TA. There had passed 388 years since Déagol had found the ring.
Are you telling me that in 2849 years, the good guys could not have found those things that Saruman did? Please.

I did read the rest of The Disaster of the Gladden Fields, of course!
Like you, I do not know why 'the good guys' didn't find more than they did. They did find the stuff Isildur threw away. Probably they didn't search that much after the first search. Why? Maybe because they figured Isildur's body had be washed to the sea? Your guess is as good as mine!
Another thing to consider is, that the Elves and Woodmen fighting the Orc party who had attacked Isidur's group probably left quite quickly after destroying and pursuing what was left of the Orc party.
Gondor and Arnor, moreover, were, just 2 years after the War of the Last Alliance and after Isildur's death in great turmoil, I assume, and the people were more interested in destroying what was left of Sauron's armies and in rebuilding their society than in searching for the remains of Isildur, which they thought had washed to the sea.