This Druid Plant Oracle is indeed out of print per a blog post I found by one of the creators, though the Animal Oracle is not. And yes, copies are getting hard to come by. EBay and Amazon listings have ranged from $70 (gone quickly) to $300 (didn't sell) just since May which was when I first really started looking to buy. Typically they're listing at around $110-$150, though if you look at eBay's completed listings, most aren't selling at those prices. But it sure makes it hard to pick up!
However, as of the date of this post, the Order of Bards, Ovates, and Druids (which is headed by the creators)
does still have it in stock at a reasonable price, shipping out of the UK. Yes, it's more expensive than list price on Amazon once was, but it's a tenth of what some people have been asking for it, and even with the exchange rate and shipping, it was still half of what the lowest priced one recently sold for on eBay.
Since I know a lot of us worry about potentially sketchy Internet sellers, I figured I'd post on my experience once the cards arrived, which happened today. My order was filled the day after I sent it in, I was able to pay with Paypal, and shipping to the Western US took about ten days. It was packaged in an oversized heavy envelope, and arrived still sealed in perfect shape. Well worth the wait to get this deck for just over $30 US.
So if this is a deck anyone really wants at a reasonable price, this is a viable way to get it while it's still in stock.
http://shop.druidry.org/Divination/ (I am not in any way affiliated with this group, just a happy customer who wants to makes sure those who still want this deck can get it for a bit longer without paying outrageous prices! They're such gorgeous cards. Now I need to get a copy of the Animal Oracle to go with it.)
Editing to add: as of July 31st, this item appears out of stock at the OBOD as well. Will edit again if someone finds this changes.