W. H. Foster is an elusive person. A W. H. or William Foster is mentioned a few times in articles around Walla Walla, WA but he was not associated with his own company much unlike Bob Naimy and Herc Picerne.
A May 9th, 1963 article about a coin show that mentioned W. H. Foster:
A May 24th, 1964 article mentioned that William Foster paid $6695 for a coin along with someone from Denver and that he was associated with the Walla Walla Coin Co.:
By doing some ancestry.com searches, I found two W. H. Foster's in the general area at the right time frame. William Hale lived in Spokane, was married to a Jacqueline, moved to Denver in 1964 and subsequently died in 1967.
William Harold lived directly in Walla Walla, was married to a Sally in 1958 but later divorced in 1971.
After talking to a retired 80 year old coin dealer recently, Bill Foster never married and the last he had heard, he was still lived somewhere in California. The dealer had said Bill Foster was not particularly involved in the company that bears his name.