You are provided the majority of source code to BillMax when you make your purchase.  You get source for over 120 executables (a small % of this count are ascii scripts),  nearly 100 or so templates or html files, plus 40 or so other configuration files. Although some source code is not provided, you have enough source to do most any customizations.  If you feel that you need source to the unavailable code let us know and we can work with you on a consulting basis. The following lists what is NOT delivered:

/usr/local/billmax/src/bin/convertpayhist.c - Convert a 1.5.x BillMax payhist table to a 2.0.x BillMax payhist table
/usr/local/billmax/src/bin/create_applies.c - Create internal financial bookkeeping records
/usr/local/billmax/src/bin/create_monthlysales.c - Create internal financial bookkeeping records
/usr/local/billmax/src/bin/manualallocate.c - Create internal financial bookkeeping records
/usr/local/billmax/src/bin/unalloctrans.c - Remove internal financial bookkeeping records
/usr/local/billmax/src/bin/licenseinfo.c - Displays the BillMax license
/usr/local/billmax/src/bin/licensevalid.c - Checks the validity of the BillMax license
/usr/local/billmax/src/cgi-bin/ua.c - The BillMax Web Forms engine
/usr/local/billmax/src/lib/billmax/*.c - libbillmax. contains proprietary algorithms core to the integrity of BillMax
/usr/local/billmax/src/lib/cgitools/*.c - libcgitools. Contains proprietary algorithms for CGI processing
/usr/local/billmax/src/lib/bmuitools/*.c - libbmuitools. Contains proprietary algorithms for bmui.cgi and bmuid communication.