You want automatic translation from another build system to gmake? I don't think that's practicable.

Or did you lose the makefile and now must recreate it from a build log?

The answer to your question: by hand. General programming principles apply here such as DRY.
Your makefile might contain definitions such as

DBDIR = /green/ppc403
DBANAMES = dbmem scnoe ...
DBAS = $(addprefix $(DBDIR)/,$(DBANAMES:%=lib%.dba))

And the recipes would use those definitions, e.g.

catalog.dnm: $(DBAS)
        dblink ... -o $@ $+

It takes some crafting. But perhaps you only need a simple batchfile?