New member as a 1903 A1 followed me home from gun show

[Dad]

The small "s" stamp on the underside of the safety lug seems to indicate a bolt of 1903 to 1912 vintage.
Check this web site.
http://www.vishooter.net/slc1_2008.html

For a replacement bolt, you could try Bill Ricca.
Check item Y49 on this web page.
Bill Ricca's 03/03A3 Parts and Accessories

D.