I'm not sure if your friend wants sheet music or lyrics.

The only in-print books I could find (there are a number of "songbooks" that are recordings) are these 2:

Bill Monroe: 16 Gems Performed by Bill Monroe. For mandolin and voice. Format: mandolin tablature songbook. With mandolin tablature, standard notation, chord names, vocal melody, lyrics and mandolin chord diagrams. Bluegrass. 48 pages. 9x12 inches. Published by Hal Leonard. (HL.690310)

Monroe Instrumentals 25 Bill Monroe Favorites. Transcribed by Todd Collins. For Fiddle & Mandolin. solos. 2000 Series. Bluegrass. Level: Intermediate. Book. Size 8.75x11.75. 104 pages. Published by Mel Bay Publications, Inc. (99962)

Both are available online through at least 2 places:
sheetmusicplus
http://www.sheetmusicplus.com/store/smp_fastresults.html?cart=33059021033153148

The-Sheet-Music-Store
http://www.music44.com/Merchant2/merchant.mv?Session_ID=4161CB190002F51D000043A700000000&Screen=SFNT&Store_Code=X

The Grand Ole Opry song folio by BM is out of print. However, a library may have a copy.
Bill Monroe's Grand Ole Opry WSM Song Folio, No. 1.
New York: Peer International Corp., 1947.
Dewey Call number: K 784.7 Monr
LC Call number: M1630.18 .B49 1947

I found that someone at http://www.bgcollector.net/ has this for sale.

HTH.

doug

http://www.geocities.com/nashville/7990/GTBmonroe.htm
--all lyrics