Here's my trick of how I was able to get ahold of a GPi.

1. Installed this browser-addin for Chrome (auto refreshes the page): https://chrome.google.com/webstore/detail/super-auto-refresh-plus/globgafddkdlnalejlkcpaefakkhkdoa?hl=en
2. Browsed to the Amazon product page for the GPi : https://www.amazon.com/gp/product/B07RT9VGS4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
3. Set it to auto-refresh every 15 min.
4. Kept the Window open so I could periodically look
5. When it appeared, I ordered :)

Might be helpful for someone so posting what worked for me. Ideally, I wouldn't have to have done this they would have had plenty of stock!

For those curious, here's the clean Amazon URL without any referral added:

https://www.amazon.com/dp/B07RT9VGS4/

https://smile.amazon.com/gp/product/B07RT9VGS4/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

Just picked one up, the original listing I had bookmarked said unavailable, but it said available new from another merchant on the listing and it took me here https://www.amazon.com/Retroflag-CASE-Raspberry-Zero-Shutdown/dp/B07RT9VGS4/ref=sr_1_2?m=A3I7DCARNWUK2P&marketplaceID=ATVPDKIKX0DER&qid=1560302823&s=merchant-items&sr=1-2 where I was able to buy

Here's the link to the Retroflag GPi CASE on Amazon -

https://www.amazon.com/dp/B07RT9VGS4/

Edit: Clean URL

https://www.amazon.com/gp/product/B07RT9VGS4/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

Link to when sales started - https://twitter.com/theetaprime/status/1136120474625282048?s=09

Retroflag GPi CASE on Amazon - https://www.amazon.com/dp/B07RT9VGS4/ref=cm_sw_r_cp_apa_i_5wG.Cb9GFFXJZ

Here is the link for the lazy

https://www.amazon.com/gp/aw/d/B07RT9VGS4/

amazon

https://smile.amazon.com/gp/product/B07RT9VGS4/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1