It turns out you will be able to buy a waterblock for Founder's Edition RTX 3080's and 3090's after all.
Bykski Releases First Waterblock for Nvidia RTX 3080 and RTX 3090 Founders Edition Cards : Read more
Bykski Releases First Waterblock for Nvidia RTX 3080 and RTX 3090 Founders Edition Cards : Read more