Go out of Llandysul on B4476 past Abercerdin Mill-house, over little bridge and turn next right. Follow road - woodland on left - past house on left, round left bend and just after house on right is row of conifers with little car park opposite.
Pull in there and follow path - well used by dog walkers by car park!
Enjoy; someone else to confirm Green woody would be geat - I have recording.
As to Brimstone I've never seen one this far west so sounds good to me