Got mine on Amazon, but a different brand than OP. Been using them since October, they work great.

https://smile.amazon.com/gp/product/B07P5R258Q/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1

https://smile.amazon.com/dp/B07P5R258Q/ref=cm_sw_r_cp_apa_i_jJDhFbN3Y33BY

https://smile.amazon.com/dp/B07NY6QXNL/ref=cm_sw_r_cp_apa_i_RJDhFbKXD82SZ

They have them on Amazon. Probably Newegg and other places as well.

https://www.amazon.com/Female-AngledPower-Adapter-Desktops-Graphics/dp/B07P5R258Q/ref=sr_1_2?crid=1F1Z9DSTFKJLN&dchild=1&keywords=180+degree+pcie+8+pin&qid=1619085537&sprefix=180+degree+pcie%2Caps%2C205&sr=8-2

• Intel core i5-9600k (Amazon)
• be quiet! Dark Rock Pro 4 (Amazon)
• ASRock Z390 PHANTOM GAMING-ITX/AC (Amazon)
• Corsair Vengeance LPX 2x8GB DDR4 2666MHz (Amazon)
• Samsung 970 EVO SSD 1TB - M.2 NVMe (Amazon)
• Corsair SF600 80+ Platinum (Amazon)

• Sapphire Radeon Nitro+ RX 580 8GB SE (craigslist)

• 180deg 6-pin connector (Amazon) https://smile.amazon.com/gp/product/B07NY6QXNL/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

• 180deg 8-pin connector (Amazon) https://smile.amazon.com/gp/product/B07P5R258Q/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

• ITX Open Air Frame Computer Case (Amazon) https://smile.amazon.com/gp/product/B07VN32196/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

• Power button + USB 3.0 (AliExpress) https://www.aliexpress.com/item/33000614029.html?spm=a2g0s.9042311.0.0.48984c4dd5KQ5t

Not overclocked yet.

Also looking to replace the Sapphire Radeon Nitro+ RX 580 8GB SE for an LE (the one w/ black and silver shroud instead of blue) or maybe an RX 5700 XT. Any suggestions?

I believe this is the kind of adapter you need..