Keeping up with foods offered by different companies is nearly impossible. And your pet may have specific requirements. Here are some websites that are very helpful…
 

Here are some results we compiled that might still be useful to you, though we have not kept up with this project.

REDUCED SODIUM FOODS (for congestive heart failure, ascites)  
Canine
(In order of decreasing sodium content)
             Nutrients of Concern (gm/100 kcal)
Product Energy content (Kcals) Na K Mg Protein Fat
Hill’s w/d (can) 359/can (14.75 oz) 0.09 0.18 0.02 5.1 3.7
Hill’s c/d (can) 436/can (14.75 oz) 0.08 0.13 0.02 5.9 6.2
Science maintenance (can) 420/can (14.75 oz) 0.07 0.18 0.02 6 3.8
Science maintenance (dry) 365/cup 0.07 0.16 0.03 6.2 3.8
Science lamb and rice (dry) 385/cup 0.07 0.15 0.02 5.3 3.7
Iams Senior (dry) 331/cup 0.06 0.18 0.03 6.5 2.8
Hill’s c/d (dry) 413/cup 0.06 0.13 0.02 4.8 4.6
Hill’s w/d (dry) 223/cup 0.06 0.24 0.04 5.1 2.1
Purina Fit & Trim (dry) 310/cup 0.06 0.33 0.07 8.5 1.7
Mighty Dog Senior (can) 150/can (5.5 oz) 0.06 0.23 0.02 7.2 7.3
Science senior (dry) 350/cup 0.05 0.16 0.03 4.8 2.8
Hill’s t/d (dry) 257/cup 0.05 0.15 0.02 4.1 3.8
Hill’s g/d (dry) 358/cup 0.05 0.15 0.01 4.7 2.8
Hill’s g/d (can) 461/can (14.75 oz) 0.05 0.18 0.02 4.3 2.4
Alpo senior (can) 388/can (13.2 oz) 0.04 0.17 0.02 6.2 5.9
Science senior (can) 400/can (14.75 oz) 0.04 0.18 0.03 4.9 3.2
Alpo senior (dry) 322/cup 0.03 0.16 0.03 4.6 2.7
Purina CNM CV (can) 638/can (12.5 oz) 0.02 0.25 0.01 3.6 6.5
Cycle senior (dry) 350/cup 0.02 0.17 0.04 5.6 2.8
Hill’s h/d (can) 538/can (14.75 oz) 0.02 0.18 0.03 3.7 6.2
Hill’d h/d (dry) 429/cup 0.01 0.16 0.03 3.7 4.3