There are two sets of numbers on the back of the radio itself....if you call your vehicle manufacturer and give them those numbers along with the VIN of the vehicle it came out of they will give you the unlock code. The dealer usually keeps it on file but if yours has closed you won't have any luck there anyway.
Most manufacturer's 800 numbers can be found here
AUTOPEDIA®: Manufacturer Toll Free 800 Numbers Directory of all automobile vehicle manufacturers for brochures, dealer locator and customer service.
Very rarely your unlock code will be written on the owner's manual, on a piece of tape in your glove box or ash tray, on the inside of your trunk lid, or even on the back of the radio-but it isn't done very often. The whole process is designed to make your stereo unusable if it is stolen from your car and if it's easy to find the code it defeats the purpose of having the code

so I wouldn't count on being able to find it.
On another note:
Do I wish I had a DIY hubby! The fact that mine is not drives me INSANE. If he were just incapable or inexperienced it wouldn't bother me a bit, but the opposite is true. In his 46 years he has worked as a carpenter, a painter, a roofer...literally a jack of all trades kinda guy-and he has made his living as a mechanic for about a decade now. There isn't much hands on labor that he doesn't have knowledge and experience enough to handle.
However, there are approximately 9,425,671 unfinished projects at my house at any given moment lol. And by unfinished, I mean that he has talked about it endlessly, made numerous trips to stores to ogle and purchase the tools and/or items to complete it, complained about it being too much trouble, and then done about 20 minutes of actual work before abandoning it forever for me to trip over until I give up and shove it all into the shed or yard.
Not much ever actually gets finished unless I either A) figure out how to do it myself or B) pay someone else to do it. I usually choose C) pretending none of it ever happened.
I'd have to laugh about it if the thought didn't make flames shoot out of my eyeballs!