Specifically what are you looking for? Do you want phrases in the Welsh language. EWQL has a word builder, I have never used it so I can't say how well it would work and you may need to experiment with some phonetic substitutions such as oo for w, hl for ll etc.
Enya is more likely to be Irish Gaelic than Welsh. Googleing Enya and Kontakt I found this.
http://www.store.precisionsound.net/avp3info.php There are some demos so you can see if they meet you requirements. (as it happens they also have a 50% off sale on until the end of the month.)
In another post you say you have Komplete on order. The choirs in the Kontakt factory provide aaahs oooha. eeehs, etc and you can morph between the vowels, they are not exactly Welsh but I suggest you check it out before parting with more cash
Tonehammer forgotten voices are a bit more specialized. I have Francesca and I will say its very good but it takes a bit of skill to sit it into a piece of music. Barbary would be your best bet for a Celtic sound, but it Gaelic rather than Welsh.
What about sampling some welsh choir CDs? If it a commercial project you would have to clear the samples of course which could be a real hassle.
Finally, if money is no object you could always get Katherine Jenkins round for a session.
post edited by Glyn Barnes - 2011/04/11 00:14:13