It's sold in December (ish) only. Personally, the people I know sitting on them are holding on to them for special occasions, but I wish you luck. Just know that if no one can help you, it won't be long before the toy vendor has them again.
I took some friends to the 2 new party spaces to celebrate my 60.
Glad I only bought the starter packs because both were rather disappointing re the lack of quoins and we didn't bother to extend, as we normally would.
I cant understand how they can possibly be described as "specially designed for sharding parties" as per the change log.