You can create your own stencils from Visio drawings (.vdx) and save the smartshapes as .vss files or libraries, which is what vdx to vss conversion essentially represents. You can do this either in Microsoft Visio itself, or with some 3rd party utility designed specifically for this. One of these for example is called PNG2VSS.
Open VDX file Open VSS fileA converter for MS Visio stencils