The International Typeface Corporation is now part of Monotype, who sells licenses for ITC typefaces directly at www.fonts.com. Adobe historically has included ITC Korinna as part of their Type Library and Font Folio, but licences for Font Folio start at USD $3000 these days.
Monotype licenses ITC Korinna directly, starting at USD $140 for a desktop licence. It would be prudent to check Monotype’s Terms & Conditions to verify that you’re purchasing the correct types and number of licences. Keep in mind that most typefoundries expect both you (the designer) and your client (the commercial user) each purchase the appropriate licences, depending on how you’ll be using the fonts.
Here’s the direct hyperlink for ITC Korinna on Monotype’s website: