OK... here's some dumb bash shit.
#!/bin/bash
i=0; z=0
while [[ $i -le 1000000000000 ]]; do
o=$(echo "lvxferre/Hello+Fediverse+$i" | sha256sum)
if [[ $o =~ ^($z) ]]; then
echo "$i: $o"
declare -g z="$z""0"
fi
if [[ $i == *000000 ]]; then
echo "$(expr $i / 1000000)M combinations tried..."
fi
i=$[$i+1]
done
Feel free to use it. Just make sure to change lvxferre/Hello+Fediverse+ to something else.
What it does: it generates the SHA256sum for strings starting with whatever you want, and ending in a number, between 0 and 10¹². Then if it finds one starting with "z" zeroes, it prints it alongside the number; then it looks for strings with an additional zero at the start. Each million tests it'll also print some output so you know that the script didn't freeze.