A red-orange sapphire is often called a Songea sapphire after the
location in Tanzania where such stones are found. Although Songea
also produces other colors of corundum, the red-orange color is
increasingly associated with that location, and almost any stone that
remotely appears “songea-ish” now gets the name. These stones usually
owe their color to high temperature heat treatment, and often
beryillium diffusion as well. They can be incredibly beautiful, but
they can also look over-cooked.
The line between songea color and padparadsha can be fuzzy, but
songeas tend to be more saturated than the the ideal padparadsha,
more red-orange than pink-orange. If you don’t mind beryllium
diffused stones there are quite a few out there these days that fit
the description. Check out ebay, there are hundreds listed as
"Songea", most are probably diffused, so look for blue spots and
avoid stones that have them. Blue spots are an unwanted side effect
of beryliium diffusion, and sometimes gem dealers on ebay will try
to make them less noticeable in the photo by covering that part of
the stone with glare from the lights.
Anyway, there are a lot more stones out there these days that fit in
the padparadsha-songea color range, due to the new treatments.
Diffused stones can be had for a fraction of the price of unheated
stones, but if you want an undiffused stone be prepared to sacrifice
either a lot of cash or a lot of color. If the stone is red-orange
and they tell you it’s heated you can probably assume it is diffused.
Hope this helps, good luck!