Once you find an authorized Denon dealer, then go to retailmenot or couponmountain!
Also check out
Fatwallet
Ultimatecoupons
couponcabin
currentcodes
Also, try asking your local Denon dealer for a discount. I've encountered dealers in Massachusetts who offer between 5 to 15 % without any hassle. And, by the way, they will not advertise these discounts over the phone or on the web. You'll have to go in, browse, and ask.