Gwenllan is a popular prefix...I found lots of other Gwenllan stallions but nothing of Brenin Du (this is probably what you've been finding) perhaps try contacting the WPCS for any info or go asking on some of the showing forums, Hamlets House for example, you will find alot of Welsh showing folk there
I have a few breeder/producer friends I will ask about but I personally couldn't find anything.
Try posting this on www.saddlesoap.co.uk its a website aimed mostly aimed at people with Welshies & there is bound to be someone on there with a pic of him
no one on saddle soap new, but thanks, its a good forum for welshie lovers! apparently theres a pic of him in the 2008 green studbook but I cant find one!
Copy and paste this - it will give you pictures of the dam and sire of Gwenllan Brenin Du so you may have a chance to follow it up from information on there - yu may be able to see pictures of other progeny - good luck