The illustrated pistol is a Warnant ("trapdoor") style Flobert, probably of Belgian make, and not very expensive when new. It is what I think of as the "least weak" of a dinky line of low powered guns.
I don't know how to get one apart, but there are only so many pins and screws to work with. Be prepared for the liklihood that the soft metal of the hammer or/and sear or set trigger engagements are just flat worn out.
If you get it going, I would recommend sticking to CB caps.