A couple websites I found helpful are realelvish.net and elfdict.com (I prefer realelvish.net but elfdict.com has been helpful at times).
Also, I suggest watching these videos:
WARNING: His pronunciation is off in the first video, especially his vowels😂 it should be:
A = AH
E = EH
I = IH as in sick. The above videos incorrectly pronounce it as EE as in machine, but this pronunciation
is used when the 'i' has a tilde ( like this: í ) above it. Thank you Elthir for correcting me (see below)
O = AW as in thOUGHt
U = OO as in brUte
and Y = Ü or EE apparently Ü is sometimes pronounced OO, but I dont really understand 'Ü' so I could be wrong lol
He goes over all these and more in the second video, but I thought I'd give you a heads up.
If you want a good dictionary, I've found
Sindarin-English & English-Sindarin Dictionary by J-M Carpenter to be really helpful.
I hope some of this helps!!