WHERE in the epistles are “minced oaths” used by any of the writers? for eg jeepers creepers, jeez, gosh, golly, gee whizz?

MINCED oaths" (euphemistic substitutes for stronger profanity) are not used by the writers of the New Testament Epistles. 
In fact, the writers of the Epistles specifically forbid such speech. The New Testament writers (such as James and Paul) commanded followers to keep their language simple, clean, and honest. 
Here is a breakdown of the relevant information:

  • Prohibition in the Epistles: James 5:12 specifically advises, "But above all, my brethren, swear not, neither by the heaven, nor by the earth, nor by any other oath: but let your yes be yes, and your no, no; that you don’t under judgment".

  • Paul's Instruction: Ephesians 4:29 instructs, "Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying...".

  • The Intent of Minced Oaths: Minced oaths like gosh, golly, gee, or jeepers creepers are described in the search results as modern, popular culture, or colloquial substitutions for taking God's name in vain (e.g., using "gosh" instead of "God"). They were typically used to avoid the strict restrictions on swearing that developed centuries later. 
    While some may argue that Paul used strong language to express anger or emphasize his point—such as calling his credentials skubalon (often translated as dung or trash) in Philippians 3:8—this is not considered a "minced oath". 
    While the Apostles did not use minced oaths, some Christians today use them, which many interpret as still violating the command to use the Lord's name reverently. Causing those who don’t use them to stumble. And the Bible strongly warns against causing another believer to stumble, which means leading them into sin, damaging their faith, or wounding their conscience. Key scriptures (Romans 14, 1 Corinthians 8) teach that love for a fellow believer is more important than exercising personal freedom or liberty, especially regarding doubtful matters. 
    Personally, I don’t even use “my goodness”because Jesus says there is none good but God, so what has “my goodness “got to do with anything!