Granted it's a tad pricey but several places have the brass in stock.
https://www.grafs.com/catalog/category/categoryId/704https://www.midwayusa.com/product/1021351919https://www.bluecollarreloading.com/products/lapua-6-5x55-swedish-brass-4ph6012https://www.buffaloarms.com/6-5x55-swedish-120-grn-hpbt-ppu6555.htmlhttps://www.precisionreloading.com/cart.php#!l=LA&i=4PH6012
https://ammoseek.com/reloading/brass/6.5x55mm
https://www.grafs.com/catalog/category/categoryId/704https://www.midwayusa.com/product/1021351919https://www.bluecollarreloading.com/products/lapua-6-5x55-swedish-brass-4ph6012https://www.buffaloarms.com/6-5x55-swedish-120-grn-hpbt-ppu6555.htmlhttps://www.precisionreloading.com/cart.php#!l=LA&i=4PH6012
https://ammoseek.com/reloading/brass/6.5x55mm