I had to do some very low sodium cooking a few years back and found that the cookbooks written by Donald Gazzaniga were very useful. They get good reviews from others at Amazon and a couple of them are inexpensive or you can get used copies. I see one is only $1.99 for the Kindle version today (the Soup, Salad and Sandwich one). I used some of his bread recipes and thought they were pretty decent. I liked some of his spice blends.
http://www.amazon.com/Donald-A.-Gazzaniga/e/B001ITVYRU
Edited to add: I also liked some of the ideas in one of Dick Logue's books. He has a few others out, though not all may be low sodium cookbooks.
http://www.amazon.com/Dick-Logue/e/B001JPBQPS/ref=sr_ntt_srch_lnk_1?qid=1453519441&sr=1-1
