shmups.system11.org

I've played a few games of Ghosts 'n Goblins (arcade version, world set 1) where the shield never spawns. Even after it sent me back a few times to play the last 2 levels, a shield still didn't spawn. Is there a trick to getting it to spawn or forcing it to spawn somehow?

Try asking one of the good people here:

viewtopic.php?f=3&t=45206&start=7980

Not to mention this big ol' helpful topic about many of our struggles with the Makaimura series. Enter at your own risk!
To Hell and Back

To answer your question (though I wholeheartedly agree that you should check out the sidescroller and GnG threads), your best bet is to farm for the shield in stage 4, off the imps that continuously spawn from the lava.

I tend to farm for the shield in the lower right corner of stage 5.
It's very likely to miss it if you don't farm for it, unfortunately. If there's a way to provoke it into dropping, I don't know of it.