C.R.
So sorry to hear about your loss, especially coming so close to the loss of your other pet. There was just an episode on "The Dog Whisperer" that dealt with this issue. It was very sweet and featured a boy around 11 years old who was so strong and wise about the process of grieving/death. I hope that your little man can learn to cope as well. And if moving right on to another pet is the best for your family, well then good luck with your search for a forever friend.
You have the right idea with keeping your options open for your new pet - look everywhere. One of the best resources for adopting a dog is www.petfinder.com It is an easy to use, searchable site where you can enter your location and what kind of dog your are interested in, and it gives you a list to start from. Best thing about this site is that there are literally thousands of different rescue agencies that collectively use this database, including the common ones here in the St. Louis area such as Stray Rescue and those that are found in Petco/Petsmart. I typed in Boxer with a St. Louis zip code and it came up with over 100 matches in a 50 mile radius just for an example.
Another great resource is www.terrificpets.com. On this website you can find some rescue dogs and many for sale dogs. There are some puppy millers on there - so research it fully. If you see multiple litters listed for one breed or someone who has 7 different breeds listed, stay away.
Despite what many people say (or imply), there is absolutely nothing wrong with buying a dog from a REPUTABLE breeder. I happen to be a reputable breeder myself (of American Bulldogs) and it really burns my behind when people imply that what I do is wrong. I happen to own show champion dogs with extensive health and genetic screening. I breed once per year - maybe - and have owners lined up who plan to show or work the pups before the pups are even born. And then, we end up birthing a litter of 10 when we were expecting 5 or 6. So, we'll have some really amazing puppies "left over" that we can sell to pet homes for a great price. You might luck into a a great pet this way. Or, quite often a good breeder will have an older female (5-6 years old) who has had 2 or 3 litters and has earned a fabulous retirement with some 2 legged kids. My neighbor got a gorgeous Golden Retriever this way.
The hardest part for you, I think, will be the sleeping issue with your son. If you get a new puppy, until it is old enough to be fully potty trained, it can't sleep in the bed. And, with an adult rescue, you need to be 100% confident that there are no dominancy issues before you let a dog up into a bed with a child. A dog's nature is to believe that if you let it up onto the couch, bed, whatever...that it has ownership over that furniture. With Rocky, I am sure that he knew his place in the home & it was perfectly safe and comfortable for him to be in bed with your son. There will be much higher safety risks with an older dog who needs to learn his place. One great way to accomplish this is to take the new dog to obedience classes with your son acting as the dog's handler. It would be a great way for your son to learn responsibility and to bond with his new best friend. (My daughter is 8 and absolutely LOVES when I let her "train" our show dogs; she thinks it is so cool.)
Again, good luck!! Feel free to PM me if you have any other questions.