Option 1 - Check the web and/or call around to local shops in your area and see who handles used wheels and/or take offs and see what they have.
Option 2 - Craigslist/facebook marketplace/whatever local for sale app or website you prefer
Option 3 - ebay
Option 4 - local flea markets or swap meets
Option 5 - buy reconditioned factory wheels through your local discount tire or other local tire shop
Option 6 - rare, but I have come across some dealers that swap out wheels on new vehicles and will sometimes sell the take offs through their parts dept at a substantial discount