GRANT statements should be generated in the DDL on the script tab, Extract DDL and migration features. Can you confirm what DB2 platform you are running this on (LUW or z/OS) and which Toad version? Thanks.
The latest release of Toad DB2 (v6.0) will display the explicit authorities as GRANT statements on the DDL tab for DB2 LUW. Toad will not display implicit authorities with GRANT statements. V6.0 should be out in several days. I recommend that you get that latest release and try it.