Deathstroke) two figure set has been out for some time now, but I only just found it this week when I picked up Solomon Grundy. So perhaps the set is being shipped in greater numbers along with 'ol Grundy now? Who knows. What I do know is that it's a Target exclusive and it's popular among fans, so grab it if you see it!
Interestingly, while Robin's mask is part of the head-sculpt, Nightwing's is a paint application. I prefer the sculpted mask but it does make each character that much more unique when next to each other.