Merlin's Power Disc release date in US and Canada at Toys R' Us is currently not known.
At this time, the only was in the US and Canada to get the 2nd CHROM Damage Increaser disc is the Race to Space pack. It is expected to release in a gold power disc pack at some point.
Click the following link for Disney Infinity Fans topic for Toys R' Us Exclusive Power Discs and UPCs
Locking the thread as question has been answered and follow up questions and answers can be done in the thread above.