I did one from amazon. Worked just fine. IKON MOTORSPORTS, Trunk Spoiler Compatible With 2017-2022 Tesla Model 3 Sedan 4-Door, Factory Style ABS Rear Wing Deck Lid https://www.amazon.com/dp/B084H6JSX7/ref=cm_sw_r_cp_api_glt_fabc_Y8DJ0YBFCAKQVVBVQF84?_encoding=UTF8&psc=1
I got this one from amazon. Fits perfect and looks good. Saw another user with it and took a chance.
IKON MOTORSPORTS | Trunk Spoiler Compatible With 2017-2020 Tesla Model 3 Sedan 4-Door | Factory Style ABS Rear Wing Deck Lid https://www.amazon.com/dp/B084H6JSX7/ref=cm_sw_r_cp_apip_kWBptyHOAwOrO
I installed a black ABS plastic spoiler designed for a M3 on my MYLR. It was $75 from Amazon. I figured if it didn't fit I'd just return it. I was surprised at how well it fit. Attached with two-sided tape.
On the M3 they say to leave 5 inches on each side. On the MY it was just over 6.5 inches. The curve was exactly the same. I am mostly looking just for the black accent on the hatchback so I'm happy with it.
https://www.amazon.com/gp/product/B084H6JSX7/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1