@nasty
There is a newer version of Blitz based on the source codes called AmiBlitz. You should probably use it instead since it contains lots of bug-fixes.
For handy links see
this forum (the board is German but this particular forum is for English speakers), and for the free download of the older Blitz Basic 2.1 and manual on a CD-ROM ISO see
Back to the Roots and look in the CD-ROM directory.