Most pet stores are pretty limited as to what they carry. I would order online if I were you.
For a lab block, I use Oxbow Foods Regal Rat. It is a low fat blend with balanced fiber and fat to help support a healthy weight. No artifical colors or flavors, corn or fillers. Since it is recommended for rats over 4 months of age, the youngsters get Solid Gold Holistique Blendz dog food. Both can be ordered online. I am able to find the Solid Gold Holistique Blendz in local petstores but must order the Oxbow online. I keep it all food fresh and pest-free using Gamma Vittles Vault Plus (15 lb size) containers.
Harlan Teklad, the best known lab block has a formula, 2018, that is 18% protein and 5% fat for young rats and nursing mothers. Solid Gold Holistique Blendz's protein is not less than 18%, not likely to be more than 21% and the fat is about 6%. So as you can see, they are very very similar. I use the Holistique Blendz because its easier to get- I can get it at Petsmart or Petco and lots of placed online. Harlan Teklad is very hard to get a hold of without buying a huge bag, unless you get smaller bags from someone who is splitting the bag and reselling smaller quantities of it. That's not a bag idea, but I personally don't like buying pet foods that are opened, especcially when I don't know how fresh it is. I also have no idea as to what the codes are on the bag, in case of a pet food recall. Seems to be a lot of them recently...
The Regal Rat has 14% protein and 4% fat, much like Harlan Teklad's 2014 formula (14% protein and 3.5% fat). This is the best of Harlan Teklad's diets to feed as an overall maintenance diet to adult rats. I buy Regal Rat online although I know other areas have said they sell it in store (my petstores don't locally).
I used to feed my rats the popular Suebee mix but I also have always had chubby rats. Now I use just the Oxbow Regal Rat and the Solid Gold Holistique Blendz as a staple and supplement my Rat Whisperer Diet Supplement, which is similar to Suebees, but each rat only gets 2 tbsp daily as a supplement, not as a diet staple. I have already seen a difference in the males weight- they don't look quite as round around the middle, LOL! You can find the recipe on my blog (see sig).
I also provide various pureed baby food, fresh and/or frozen fruits,veggies, and fresh herbs including but not limited to:apples, bananas, prunes, peas, corn, bok choy, fresh parsley, carrots, broccoli, cauliflower, celery, melon, dandelion greens, green beans, dark leafy greens, various berries, etc. I try to alternate fruit, veggie, fruit, veggie, etc.
Three times a week they also get Healthforce Nutritionals' Green Mush, a superfood.