Amazon has it available to rent for $3.99.
https://www.amazon.com/Kingdom-Heaven-Directors-Roadshow-Version/dp/B00UMD560E
Otherwise, I’m sure you can find it on some other sites, but make sure to look for the “roadshow version” as I think that’s what the director’s cut is called. If there’s any doubt, the roadshow version is 3 hrs 13 min vs the theatrical release which is 2 hrs 24 minutes.
Amazon Prime (US) has it:
https://www.amazon.com/Kingdom-Heaven-Directors-Roadshow-Version/dp/B00UMD560E
https://www.amazon.com/Kingdom-Heaven-Directors-Roadshow-Version/dp/B00UMD560E
If you want to play pirate you could also find it