Got a call from my local Texas GameStop today, letting me know that The Black Series 6" 40th Anniversary R5-D4 figures I preordered arrived today and is ready to pick up. While picking them up I asked if they received a lot of these figures to sell and he said no, they only received 2 figures which were shipped in a 5 foot tall 40th Anniversary Cardboard Display which also included TBS 3.75" Die-Cast Figures & Vader 6" Legacy Pack as well. (Display was still in the back room, so couldn't take a photo of it)
Out of curiosity, I asked him if he could check stock at some other store locations, so he did and he stated that it looks like all the stores in this Region only received 2 figures for this first shipment. Now I am not sure if this is Nationwide or not, but it looks like if you were not the first or second person to preorder these in store, you may have to wait for a future shipment.
Also GameStop.com has taken down preorders for this figure at the moment, but the "Pick up in store" option is now live, so you can try and track one down by putting in your zip code.