The G-Shock GA-2100 series was the most successful new G-Shock model of 2019. The all black GA-2100-A1 (GA2100-1A1 in the U.S.) was the most popular colorway by far and sold out shortly after its release. In 2020, some U.S. retailers have received more stock, but the watch is still selling out quickly, and it is usually available only sporadically.
We suggest checking the link below, as the official G-Shock U.S. site (gshock.com) has been restocking it regularly, more than other retailers.
G-Shock GA2100-1A1 Stock Status in the U.S.
August 2021: In stock at gshock.com in mid-August. In stock at Bloomingdales.com.
July 2021: In stock at Zumiez.com, along with the gray GA2110ET model, as of July 5. In stock at gshock.com, as of July 9. In stock at gshock.com again on July 22.
June 2021: In stock at gshock.com as of June 7.
May 2021: In stock at gshock.com.
April 2021: In stock at gshock.com as of April 2.
March 2021: In stock at gshock.com as of March 6. And again as of March 13.
February 2021: gshock.com has it in stock again (as of February 3). And again as of February 18.
December 2020: Zumiez currently has it in stock again (as of December 29).
November 2020: The GA2100-1A1 was available again at gshock.com in late November, but as we write this, there is only one left.
October 2020: gshock.com has it in stock (as of 10/22). gshock.com is showing the “Buy Now” button (as of 10/7) but says it is out of stock after clicking it.
September 2020: The GA2100-1A1 has been available sporadically at Reeds Jewelers in late September. Gshock.com was showing the “Buy Now” link in early September. Kay Jewelers had it in stock in early September.
May 15, 2020: The GA2100-1A1 was in stock at Reeds Jewelers for a very brief time.
May 1, 2020: The GA2100-1A1 was back in stock at GSHOCK.com.
April 29, 2020: The GA2100-1A1 was reportedly back in stock at Reeds.
April 14, 2020: The GA2100-1A1 was in stock at authorized dealer Reeds Jewelers.
UK Update: G-shock.co.uk had the GA-2100-1A1ER back in stock, but it sold out quickly.