You probably won't find that exact mix, especially as a puppy at the pound, but I'm sure you can find a mastiff mix or a rottie mix. And is there a reason you want a male? Is it because her last dog was a male? Don't expect that if you get a mastiff/rottie mix male it'll be just like the old dog. All dogs are individuals. Whatever dog you get though, with love and training, he or she will turn out to be a wonderful dog and companion for your mom.

Here's some around your area:
mastiff mix pups
female rottie mix pup
small rottie mix puppy
pretty rottie/aussie mix pup
purebred female rottie pup

Good luck on your search!