I would go to the
GW site and look through the Warhammer fantasy figs. They tend to have a lot better shields than
40k figures, and they're a bit more prevalent. The shields also have a bit more of a heraldric look, which definitely fits in with the Space Marine look a little better than some of the
40k shields.
As to the spear, I wonder if you couldn't find some kind of giant bird fig, (I know they have those in Warhammer fantasy) saw his leg off, and then bend/cut it down to only three claw-toes, mount your severed bird foot on the end of a pole (I use lollipop sticks, available in your friendly neighborhood craft store's cooking section) and paint it in metallic colors to make it look like a kind of stylized trident? Would that maybe work for you?
Here's some pictures of my figs, where I am using Warhammer fantasy shields, as well as lollipop-stick poles. (The big spear is intended to be a relic blade, in point of fact.)