I know this isn't the answer you want but the answer is it depends what you are looking for. There are very few sites that have "in stock" aluminum cases that you can buy and have it shipped to you in a reasonable time.
If I were you and cost isn't a factor and you do not wish to wait, your best bet is to buy from the Mechmarket subreddit.
If you don't mind waiting, joining a group buy on here (Geekhack) is probably your best bet. The 'Group Buys and Preorders' category is where you can find the most up-to-date group buys.
You can also join the mechkey group buys Discord.
