If you can't go out to get a replacement, you could manually express the milk by massaging your breasts. It will not be comfortable though, I'd imagine you have to stand or sit at an awkward angle to express the milk into the bottle. I read from a blog somewhere (can't remember for the life of me which) that a mommy had the same torn spectra valve problem. But lucky for her she had a broken medela pump lying around. She took the valve from the broken Medela and apparently it fits into the spectra. She was back to pumping normally.
Do you have any other pumps at home? Try swapping the valve with those valves, for eg the Medela or freemie valves can be swapped with the spectra. otherwise unfortunately you need to pump one side first and then use the valve on the other side when you have drained one boob.