I'm having trouble finding an available switch to match a schematic. Is it possible?
If you can tolerate a rotary switch then it's easy.

Figure 1. A 12-contact rotary switch by Lorlin.
These switches have 12 contacts around the edge and 1, 2, 3, 4 or 6 contacts on the inner ring to make (respectively) 12-way, 6-way, 4-way, 3-way or 2-way switches. (You have to order the right version. You want a 3-way.)
There's a washer with a stop-tab that is inserted on the threaded boss to limit the number of positions it can be turned to.
Variations of this type of switch have wafers which can be stacked to give a wider variety of switching arrangements. These were popular on old radios and oscilloscopes.