From the book, "Names on the Face of Montana: The Store of Montana's Place Names," by Roberta Carkeek Cheney, first published in 1983:

"LEWIS (Madison County) had a post offie (1873-83 with Paul Hayward and John Scanlan, postmasters. Lewis was a mining camp near Norris, but nothing more is known about it. When the office closed the mail was forwarded to Red Bluff."
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This is all the information I could find. I was unable to find anything out either Mary Anne or Paul Hayward. Hope it helps a little bit.