I think the IO asked about any violations or tickets or something to that sense, and I offered the information about the tickets. ( Also to note, that I had not mentioned those tickets on my N400).
Certified disposition letters are issued by the municipal courts where you paid your ticket. It has a court stamp and certificate that the ticket(s) have been disposed off with the fine mentioned. I understand you do not have any information on the ticket numbers or anything, so that may be difficult to find. But as suggested otherwise, if you can get a county search or something done and get the ticket number or the date, that may work. But in general I agree with Mike E that it is un-necessary hassle IOs put us through, especially when you do not have any serious record like drunk driving, accidents etc.