They appear to be rare if you read into the following threads:
www.elitefourum.com/t/japanese-boosters-collection-only-miss-one-to-be-happy/32248/1
www.elitefourum.com/t/is-this-the-rarest-charizard-that-exists/31801/1
But who knows, there’s also this thread where someone is managing to buy the cards for $10-20 each.
www.elitefourum.com/t/wtb-uled-wcp/34121/1
If you have packs for sale holla at me.