What type of bonding is there among d-block metals?
Unpaired electrons are not the only thing that are used for bonding in d-block elements. The outermost ns electrons are also present for bonding.
     and when you ask what type of bonding is present in d-block elements, it means you mean to ask the type of bonding present only amongst these metals, and not with some other element(like p-block elements, say F, Cl). If that is the case, then only metallic bonds are present in d-block elements. For example, copper atoms are held by metallic bonds in the metal crystal.

The factors affecting the strength of a metallic bond are-


No. Of valence electrons (more number means higher attractive forces, and hence stronger bond)
Distance of ionic core from the valence electrons (lesser distance means a smaller size of the metal ion, and hence higher value of the force)
Presence of vacant d-orbitals (the free valence electrons in metal travel through the metal crystal using these vacant d-orbitals. So, if there are more number of vacant d-orbitals, the free electrons are more easily "accessible" for attraction by the ionic cores)