The original implementation of SPITBOL, for the IBM 360, has been available in source form under the GPL license since 2001, from www.snobol4.com/spitbol360.
The SPITBOL Project has just republished these files in a GIT repository: github.com/spitbol/360
With the publication of this version, the source for implementations of SPITBOL produced over a period of over forty years, for the IBM/360 mainframe, MS-DOS for 8088 through Pentium chips, unix for i386, and unix and osx for x64 (amd64), are all now available from github.com/spitbol.