Be a TRUE Star Wars fan and rock out to These exciting Droids animated shows!
I grew up with these that begin with this episode, "The White Witch," originally airing in 1985!
The EU has apparently explained that Captain Raymus Antilles lost R2 and C-3PO for a while, between ROTS and ANH, but they made their way back to the Tantive IV and served his son, Captain Colton Antilles (named for the Tantive's pilot, Colton, played by Jeremy Bulloch in ROTS).
In "The White Witch," C-3PO explains that the Droids were lost to a smuggler in a gambling debt, and then the smuggler's ship was raided and destroyed (by the Empire looking for Rebel contraband?).
The EU could further expand on this, if they decided to do a post-ROTS TV show.
Meanwhile, enjoy the cartoon. THIS IS A GEM!