Does anyone know where I can source cardboard oven proof and microwave safe pie dishes and if these are even possible?
I'm not sure whether they are sold for consumer use, but I can say that Amy's brand pot pies come in a cardboard pie pan with instructions for microwaving or baking in a conventional oven. So they do exist.
Whether such pie pans are suitable for start-to-finish creation of a pie is another question, I'm fairly sure the Amy's pies are partially prepared and then transferred to cardboard pie pans (possibly after they're frozen).
For home cooking, a glass pie pan would be an option if you need to bake a pie in the oven and then heat it later in a microwave. Depending on your oven, you may need to be careful to place the pie pan on a metal tray, or put a metal tray on the lower rack below the pie pan to prevent radiant heat from over-cooking the lower crust of the pie. (Edit: On second thought, a baking stone would probably provide a better radiant heat barrier.)