I have really heard these Tolkien names with the wrong stress

You will get the complete list at the end, here we get started with correcting it.

You recall the rules. In words of three or more syllables, the length of last or third last syllable are immaterial, the important thing is the length of the second last syllable - stressed if long, following the stress if short.

A long syllable is one which a) has a long vowel, including a diphthong, or b) has a vowel followed by two consonants, including double consonant, excluding muta cum liquida.

Muta cum liquida are P, T, K (C), B, D, G or even F followed by (and not following) R or L.

Mórinehtar. HT = German ach-Laut plus T (or ich-Laut plus T).

This means the second to last syllable has the vowel E followed by TWO consonants, namely HT. They are not muta cum liquida, so the stress is on the second syllable.

Elessar. SS = long S, counts as two consonants, so, the second E is followed by two consonants that are not muta cum liquida. Hence, if you look for a rhyme on Elessar, try "lesser".

Isildur and Imladris. Their stress patterns get reversed.

With Isil and dur as two consecutive words, the stress would arguably be on the first and last syllable, but* when they are put together as one word, a name, the second I is followed by LD, two consonants, and they are not muta cum liquida, but on the contrary, liquida cum muta. So, Isildur would rhyme (very roughly) with Tilda.

In Imladris on the other hand, DR are precisely muta cum liquida, so, the second syllable is unstressed. This gives the first syllable the main stress - and the last a subsidiary one. If you want to rhyme on Imladris, try "kiss" or "miss" - though it's a bit sloppy to end a line in English with just a subsidiary stress where a main stress should be.

If the A had been long in itself, it would have had an accent (á, like the ó in Mórinehtar). So, the A is short in itself, it is followed by muta cum liquida which kind of counts as one consonant, because the muta adds so little to the liquida, so, it is unstressed as said.

If you want external confirmation, take the line:

In Imladris it dwells;

It should be pronounced, in exaggerated scanning, as:

in IM la DRIS it DWELLS

because all the other lines have three stresses. Here is a correct scan of the entire** poem:

SEEK for the SWORD that was BRO-ken;
in IM la DRIS it DWELLS;
THERE shall COUN-cils be TA-ken;
STRONG-er than MOR-gul-SPELLS.
THERE shall be SHOWN a TO-ken
that DOOM is NEAR at HAND,
for i-SIL-dur's BANE shall WA-ken,
and the HALF-ling FORTH shall STAND.

It doesn't help for Isildur, the wrong pronunciation would still be metrical, the line would either way have three stressed syllables, but you can see that the second line of the first half has the same rhythm as the second line of the second half, namely:

in IM la DRIS it DWELLS
confer
that DOOM is NEAR at HAND

None of the lines has just two stressed syllables, so the wrong pronunciation of Imladris is atrocious to the metre.

Mórinehtar, Elessar, Isildur and Imladris - next time you read them, you know how to pronounce them. Incidentally, in the English original, Tolkien is a great poet.***

Hans Georg Lundahl
Paris
All Hallows' Eve
31.X.2022

It seems the separate word for finishing -dur or -ndur in Quenya is actually núro - servant. Nothing with d- in Quenya. Original d- become l- and original nd- become n- - but get the d back in median position, either with or without n, -nd- after vowel or -d- after r or l./HGL

PPS - two more, but this is not about placing of the stress accent. Uinen and Cuivénen involve the diphthong UI - it is not meant to be WEE, but OOY, please!/HGL

* Consider in English how "insight" has stress on IN, but (in US or parts of) "insightful" has stress on SIGHT.
** The Barrow-Downs Discussion Forum : Faramir's (and Boromir's) Dream
http://forum.barrowdowns.com/showthread.php?t=12756
*** This is not the case for all translations!