I don't have a particular site or information source to share, but do find often trade associations have sample job descriptions. I find templates and samples to be a good launch pad. Best used as a place to start thinking about what YOU and YOUR COMPANY expect and need from a certain position.
I have some that I have used over the years. They arent templates, but they are a good place to start. I also have always used what I call a Job Clarification Form, where the employee fills out what their duties and respnsibilities are and then write the descriptions, with editing as to what management wants those positions to be doing.
Contact me with the ones you're looking for and I'll see if I have them.