Is there such a thing as a momentary SPDT off-on-on switch? "off-(on)-(on)"
Sort of, this kind of switch is commonly used as a shutter release for digital cameras.  They are not the old style toggle type but they work more like tactile momentary type and rely on two different pressure levels to operate.  A half press is used to activate the auto-focus and then fully pressing it will take the photo.

Questions about where to buy stuff are off topic but hopefully this gives you a starting point.

If you definitely require an old school up-middle-down lever style toggle then you can get units that are user configurable, where you need to open it up and move the contacts and springs to suit your needs.  These are expensive of course.