Re: need STE53NC50 MOSFET PSPICE library
I guess, searching a similar transistor or paralleling several lower current devices will be the most easy way. The other available method is using the PSpice Model Editor tool and needs basic characteristics like Rds,on and Id versus Vgs and capacitance numbers.
As an additional remark, for a reasonable simulation of circuit behaviour, you posibly need to add package parasitics, particularly inductances. They are not considered in most basic vendor and PSpice shipped models, although some have it, e.g. from ST.