Coupon clipping services are the most direct way to "buy" specific coupons. You aren't paying for the coupon itself (which has no face value until redeemed), but for the labor of the "coupon fairy" who sources and clips them for you.

: Another established service for ordering manufacturer coupon inserts in bulk.

Most modern couponing has shifted to digital platforms that are free to use but offer the same (or better) savings than physical "bought" coupons. RetailMeNot