My father went through something similar and we all started noticing how much sodium was in food, and it really was shocking. Even something as simple as cottage cheese contains a lot of sodium.
Are you familiar with the Rice Diet? It's not rice as in the grain, but as in Rice University. It's a very restrictive weight loss diet, but it's also very restrictive in sodium. They have a book and cookbook available that offer tons of tips for reducing sodium in foods and is really helpful. I think the American Heart Association also has a low sodium cookbook out.
There are good alternatives out there, but sometimes it takes searching. For example, Old El Paso salsa has about 230 mg sodium per 2 Tablespoon serving. But some other brands, such as Frog Ranch, contain just 40 mg and taste fantastic.
Good luck to your FIL