Hi Pomegranate7224. It's now several years after you asked about Communion Restaurant, but I thought you might be interested to know that there is a book which briefly discusses its founding and history. It is called "Honest Business" by Michael Phillips and Salli Rasberry, published in 1981 by Random House. The history of Communion Restaurant is discussed in Chapter 7, and the restaurant is mentioned again in Chapter 10. (It might be in later chapters too, but I haven't finished reading the book yet.)
Learning about Communion Restaurant has been fascinating for me, and I highly recommend finding a second hand copy of Honest Business (it is out of print).
I hope you find this message.
Best wishes from the UK.