The Art Store has a considerable amount of mediums and varnish for both oil and acrylic paint.  Mediums can be used for a number of things:  Extending the life of your paint, slowing the drying process, crackle effect, impasto techniques, adding texture, glazing, etc.

Varnishes are the final coat you lay down when you’re painting is finished.  The Art Store carries matte, satin, semi-gloss, and gloss varnish that can be applied with either brush or spray.