So it looks like Star Wars Black Series collectors will have another 6" set to pick up at SDCC 2016. As we suspected, when the images showed up a month or so ago, the 3 pack of Astromech's are indeed going to be an SDCC, but through Toys R Us.
"You'll only find these items online and at the Entertainment Earth Booth #2343 at the summer's largest Comic Convention in San Diego, CA!" - Toys R Us
The online statement in the above quote from Toys R Us does give hope to collectors not attending SDCC, and in certain cases TRU do ship internationally.
Build your Star Wars collection with the Astromech Droid 3-Pack from The Black Series! This collectable showcase of the heroic droids from the Battle of Yavin features exquisite craftsmanship, multiple points of articulation and premium detail that only The Black Series from Hasbro and Star Wars can offer!
As we originally posted, the breakdown of the set is as follows
R2-A3, an R2 series astromech droid used aboard Wedge Antilles' T-65 X-wing starfighter
R5-K6 , an R5-series astromech droid that was built by Industrial Automaton and belonged to Garven Dreis, the leader of the Rebel Alliance's Red Squadron (A New Hope)
R2-F2, is the interesting one as he is listed on this box as being the R2 unit who flew with Biggs at the Battle of Yavin. In fact Biggs droid was R2-Q2, and R2-F2 was only added to the Star Wars Universe via the X-Wing Miniatures game.
They all seem to be based on the original wave 1 R2-D2 mould, with new R5 head for K6. There seems to be plug in accessories down the side of each droid.
(source : Wookiepedia)