On the other hand though, I think almost everyone finds the drowned troll inadvertently. It's not hard to miss though.
I've never found it. I was going through the UESP looking for easter eggs one day and found the troll entry. So I went looking for it, but no troll! I've looked further up the river, too, but I still can't find it.
I would like to know however, how people first became aware of such an item. I highly doubt Bethesda just shouted out to the world, so some very bored and strange person must of either looked through the Item list in the Construction Set OR, and more sad and impressive, explored the underwater reaches along the coast.
Any speculation?
I'd say someone decided to go for a quick dip and happened across the helmet.
Or someone was modding and looking through the Glass Armour and found
DarkFInGleam they wondered what it was and found out its base info etc.