https://www.aliexpress.com/item/Bykski-A-MS58GMX-X-Full-Cover-Graphics-Card-Water-Cooling-Block-For-MSI-RX580-Armor/32926543078.html?spm=2114.search0104.3.2.1d2610c8X58ukq&ws_ab_test=searchweb0_0,searchweb201602_6_10065_10068_319_317_10696_10084_453_10083_454_10618_10304_10307_10820_10821_537_10302_536_10902_10059_10884_10887_321_322_10103,searchweb201603_16,ppcSwitch_0&algo_expid=1878807f-ac64-40aa-82c4-e5309aa661ae-0&algo_pvid=1878807f-ac64-40aa-82c4-e5309aa661ae
Basically no uses reference PCB for the 580 from what I know, so you need a block specifically for your card, which is why there are so many and why EK doesn't bother. The above one fits an Armor 580, so should be fine I think?