Andy Hughes, CC>CC member and Las Vegas, NIS provider has announced that previously used $4 drop chips from the poker room, were available for purchase at the same time the Imperial Palace released their Halloween LE's. Previously very hard to get, these chips are available from Andy, as linked in the scan credit, below.
As a drop chip, these are not used for game play. They typically sit in the dealer's rack and instead of dropping the rake from collected chips in-play, the dealer will instead use a drop chip and replace that minus amount from the in-play chips.

(scan courtesy of:
http://www.nevadacasinochips.com/ )
Jim (Gaming Ore) Follis