These are keshi figures. They came from gachapon machines in Japan. There were several series, from Super Bomberman 2 through 5, Saturn Bomberman, and more... The ones you're looking at, from the Super Bomberman 4 Guidebook, have been painted. You'll likely be buying unpainted ones if you can find them.
Places like eBay are your best bet. People sell keshi there all the time. It's just a waiting game, really. My own collection has taken years to amass, and I'm still collecting. You'll have to fight me for any that I don't have, though. :P
Here, I have Jet Bomber and Great Bomber. This is what they look like. In my hand, you can gauge their relative size.
Man, thank you for the info. I'm so envy of you....
I think these two are the hardest to find. I saw a jet bomber on ebay but the jet pack at the back is missing. I was thinking if I should make a custom one but no idea how to make a pretty one (maybe with light weight clay?).