I found Bert in Stanley, Custer county, Idaho. He is indexed as "Ben" or "Paul", but appears it could easily be "Bert".
1920 census, Stanley, Custer, Idaho. SD 1, ED 73, Sheet 4a. Dwelling #11, Fam #11. Date of census: 10 Mar 1920.
Bert Buchanan, W/M, owned residence, 33 yr [c.1887], b. NC, mail carrier/courier for Stanley ____ [can't read].
wife: Jennie, age 27 [c. 1893], born Utah, father born Missouri, mother born Utah
dau: Bradinia [?? difficult to read], 7 yr [c. 1913], b. Idaho
I saved a copy of this census page to my computer. Drop me a note at bethpany at yahoo.com and I'll be glad to send it to you.
I could not find any of them in the 1930 census???