Replacing the boards is the easiest and quickest way.

Yeah, that's not coming out without a full sand and even then there is no guarantee.

I think that is a little harsh ^^^^

I don't have any experience but found this. Different methods for dog and cat urine (who knew)? I'd try a tiny little spot (maybe a spot using each method) to see what happens before diving in fully:

What is the best method to remove black dog urine stains from hardwood floors?

Remove black dog urine stains from hardwood floors using hydrogen peroxide. Soak a clean cloth in 3% hydrogen peroxide and rub it on the stain. Then place an absorbent cloth on the stain and saturate it with peroxide.

Let the peroxide-soaked cloth sit on the spot until the stain fades away. Finally, wash the floor with water and pat dry.

What is the best method to remove black cat urine stains from hardwood floors?

Baking soda and distilled white vinegar will remove cat urine stains from hardwood floors. First, mix baking soda with vinegar to get a soft paste. Then rub the paste on the stain using fine grade steel wool.

Apply more paste and let it sit for an hour. Wipe off the residue with a dusting cloth.

G&S is right. Hopefully you can find some boards to use for replacement. No point in trying to sand and bleach because neither is likely to help.