If you live in a rural area, you may be able to get cow or pig blood from a local farmer when he's slaughtering an animal. The recipe I came up with would also look great for your exercises in estimating blood loss. This was a good tactile and visual example . You might suggest that they make red jello and then try pouring measured amounts on pads, towels, jeans, etc. I find that people who don't put away food often have a problem estimating blood loss because they are not used to judging volume .
Different pads hold different amounts and different size pads hold different amounts .
I don't know if this would be appropriate for paramedics, because they probably wouldn't have chux pads around in an emergency birth scenario, but this is how I was taught . And just heft the chux and 'feel' how heavy it it. After a while you get a feel for it, and if you're using food coloring you can get a pretty good eye for it too. But I always lift the chux, just to verify what my eye thinks it looks like. When I was a midwifery school, the instructor used red jello, partially congealed in bowls and asked us to estimate the blood loss.