The simple and short answer a response of the Prophet () is not quoted in any of both Sahihs (neither in Sahih al-Bukhari nor in Sahih Muslim).
In fact they only quoted the jealous reaction of 'Aishah as you may find in your finding Sahih al-Bukhari and here in Sahih Muslim. This lead some scholars to the interpretation that the prophet () let these words pass without answering them. Ibn at-Theen (or at-Thyn) ابن التين (*)
(*) a scholar ibn Hajar has quoted in his Al-Isabah calling him Muhammad ibn 'Abdalwahid as-Safaqusi محمد بن عبد الواحد السفاقسي while the aiuthor of the book on authors and their literally remains Hadiyat al-'Arifyn هدية العارفين أسماء المؤلفين وآثار المصنفين 'Abdulkwahid ibn at-Theen or at-Thyn as-Safaqusi (from Sfax) a maliki scholar, both agree that he was a commentator of Sahih al-Bukhari which was called al-Mihbar al-Fasyh المحبر الفصيح في شرح البخاري الصحيح which is not available in printed version, according islamweb #81506.
said the fact that the prophet () remained silent about the words of 'Aisha is an evidence that she actually is better than Khadija except if it what was meant with "being better" was the beauty and the low age. Ibn Hajar al-'Asqalani after quoting this -in his fath al-Bary, see here in Arabic- added in fact an answer has been reported: In the narration of ibn Najeeh from 'Aisha whish was compiled by at-Tabarni in his al-Kabir (See here and another one here in Arabic) and al-Musnad of imam Ahmad (See for example here in Arabic), I found it in al-Hakims al-Mustadrak too -see here in Arabic- the prophet's () anger and reaction was of such a kind that 'Aisha decided to never mention her name again except in a good and nice manner. And a second narration via Masrooq with the response you've provided again in Musnad Ahmad (See here in Arabic) and at-Tabarni's al-Kabir (3 times see for example here in Arabic). The narration of imam Ahmad has one dai'f narrator (Mujalid ibn Sa'id مجالد بن سعيد) while the other narrators are of higher level of trustworthiness. This same narrator appears as one of the weaknesses of at-Tabarnis narration. Ibn Hajar added that the statement of the first response is in accordance of ibn at-Thyns interpretation.
The prophet () in the first recorded response made clear that none of his other wives was able to give him what she (Khadija) gave him referring to children, before getting angry.
I think the statement of ibn Hajar shows that your search result and mine are correct a response doesn't appear in any of the both Sahihs.