You can buy one in the Black Pits and then import it into the actual BG:EE game by either using that Pits character in a BG run, or doing a little sideways trading and importing with your BG character before starting the actual run.
There is one in The Black Pits standalone module, but not in the main game. Ironically it's almost useless in TBP as you get fully healed at the end of each round.
If you want to regenerate then it is possible, but slow. Either roll a Dwarf or Half-Orc with 19 constitution. Get the tome which increases constitution by 1. At 20 Constitution you regenerate 1HP per minute. Travelling or resting will then fully heal you.
If you use Buckley's Buckler (+1 con while equipped) sold at the Friendly Arm Inn you can use this regen with most characters with a starting Con of 18.
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If you want to regenerate then it is possible, but slow. Either roll a Dwarf or Half-Orc with 19 constitution. Get the tome which increases constitution by 1. At 20 Constitution you regenerate 1HP per minute. Travelling or resting will then fully heal you.
If you use Buckley's Buckler (+1 con while equipped) sold at the Friendly Arm Inn you can use this regen with most characters with a starting Con of 18.