I recently did a Google search on "dry stacked pizza oven". There were several interesting designs.
A person with a little ingenuity could buy a bag of castable refractory (not insulating type) and make stringers to bridge the critical area. The form would be of the same with and thickness as a brick but longer, to suit. If you try this -do not- use reinforcing metal inside the brick since the rate of expansion for commonly available reinforcement metal is greater than the refractory. The blocks will crack. High strength castable refractory sometimes comes with stainless steel needles which add strength.
There are many manufacturers of castable refractory and each seems to have six or eight different products depending on the end use. I'd go for a one that has good strength since it will be supporting bricks from above. An option would be to cast a simple roof slab and lay it atop the dry stacked sides. I thought of making a semi-permanent dry stacked pizza oven and covering it with a layer of perlcrete for insulation. The insulation could easily be removed at a later time if it wasn't mixed with too much portland cement.
Look for castable refractory cement at a building supply (Not Lowe's or Home Depot), Kiln supply or possibly a welding supply, since metal workers often build simple forges for home use.
The pizza and bread baked in one of the dry stacked ovens looked good. The concept proves you certainly don't need a $4000 pizza oven or huge, domed, masonry, piece of art, to make pizza and bread.