You can do a search of this forum and find more info on the topic. I have the same machine and you do not need to purchase a non-pressurized portafilter. The pressurized portafilters can be converted by dismantling the handle and removing the plastic mechanism, the false floor and the rubber o-ring seal.
If your original one is broken beyond repair then you could always just buy another pressurized portafilter and do the conversion.
Someone else might know where to source a new non-pressurized one or if another brand will fit the head.