Hi, I haven't found out the answer but thought I'd post the likely date and location for an obituary for Richard Blair Madsen. His obituary would likely list his offspring.
Richard was living in Lewiston, Nez Perce, Idaho in 1935. In 1940 he was married to your mother and living in Portland. The census says he was born in North Dakota. Any previous residence could also be a location for an obituary for him.
Find-a-Grave has a memorial for him at Willamette National Cemetery in Portland. No wife and children are listed (as is typical with Find-a-Grave memorials). He is noted as a vet: MSGT US Air Force, World War II, Korea. If you search this cemetery for other Madsens and check the burial plot you may find any second wife he may have had.