I constantly get asked Where Is The Rogue One 3.75" Galen Erso Wave? Per Hasbro this wave has already shipped out to Retailers (though they wont state who) but they mentioned to keep checking online retailers such as Amazon. Also this wave is the last wave of the Rogue One Toy Line, so production of this wave has been reduced as well.
Up to this moment I have not seen any preorders for this wave and I have only seen this assortment in stock and sold by one retailer so far and that was CMD Store which sells both out of Canada and the US. Right now they are offering a set of 6 figures for $59.99 plus shipping. I personally did buy a case from this company and it arrived mint.
Now the bottom line is I am not sure how hard this wave will be to obtain and I am not telling you to run over to CMD Store and spend $60 on it, but it is a a option if you are worried on missing this wave. Who really knows, this wave may show up at discount Retailers like Five Below and etc after all.
Update: They are sold out as of now.