For form 8885 where do you get... An official letter reflecting that you were an eligible individual for the months claimed on line 2 in 2017?

[Critter]

If you don't know what that letter looks like then you probably didn't get one and you are not eligible for the credit you took ... they are mailed out in January.   https://www.irs.gov/credits-deductions/individuals/claiming-the-health-coverage-tax-credit