3D printed samples
You can 3D print couter mold but for some specific use it is also possible to directly 3D print samples. This is not an easy task because you need firts to find the proper material to 3D print and you then need to print your sample without adding residual stress. Let's state it, it is not the best way to have singularly shaped proper photoelastic sample. If what you are looking for is a you prefer to use the method described here
Still when you want to rapidly prototype a photoelastic material and if your measurement accuracy are not too high, it still worths.