I want to start a business that sell a product and donates a portion
of the sales to a charity or some qualified 501 org. I want to know
where I look to find out if I can give the purchaser a tax deduction
on that portion that goes to charity? Or who do I got to to get more
info on this topic.

I'm not sure what the ramifications on giving it away are, but you
won't be able to double-deduct.  That is to say, if the purchaser gets
the tax deduction, you can't also get it.

It would probably be wiser to have the purchaser pay full price and
have you deduct the donations from your (or your business') income. 
This will most likely be advantageous to your (or your business') tax
situation.

This is all very general; For specific numbers, you'd need to
obviously consult an accountant and/or tax attorney.

Won't the purchaser need a receipt from the charity to claim the deduction?
Neither you nor the charity can "give the purchaser a tax deduction".

NO.

You cannot pass on the tyax deduction.  Take the tax deduction
yourself.  Or better, dont give to a charity and charge a lower price
so your customers can give their saving on to a charity of their
choice and deduct it.

Your idea is noble, but it doesn't work.