Hi Nao,
I only had my interview today, so I hope I can offer some answers, and hopefully I am not too late.
One of my biggest fears leading up to this moment was that I had answered "No" to question #23 of the N-400, i.e.: 23. Have you ever been arrested, cited, or detained by any law enforcement officer for any reason?, but just a few nights before my interview, came to learn that traffic tickets do indeed quality as citations (I should have known this, but the way that question is worded makes me think about actually being detailed rather than being cited for speeding). So, I had to look and scrounge around until I figured out how to look up my ticket online, then had to search for the court system in my emails to find proof of payment.
To address your questions/concerns, I believe the most important thing to realize is that mistakes happen, and most immigration officers (IOs) are not necessarily out to get you (although temperament varies). So, if you can help it, do not panic too much just because you cannot find the ticket or proof of payment -- what is important is that if the question about citations comes up, you ask for clarification (that is what I did when they asked me) on whether citation includes traffic tickets. If the answer is yes, then state that you recall getting a ticket, but cannot to the best of your recollection remember exact dates, nor could you find the proof of payment. Normally, they will just note what you said, and move on. It is rare for them to make a big deal of a single traffic ticket or treat it as dishonest since most people often overlook the tickets.
In my case, after gaining clarification that citations included tickets, I told the IO of my ticket, then she asked me if I remembered any dates or other pertinent data about the tickets. Luckily, I was able to then produce the tickets and proof of payment, but based on what I gathered, and the way the IO reacted when I asked to amend my original answer (that is, change the answer for question 23 from no to yes), she wasn't really expecting me to know/remember the dates, but wanted to jot something down about why we had to change the answer. Mostly, she was just looking to confirm that it was an honest mistake and even reassured me that this particular change had no bearing on my overall case. So truly, Nao, I know it is difficult to imagine, but do not let this deter you from focusing on other aspects of the interview. If the question (for citations) comes up, answer it truthfully and you will be fine. If the question does not come up, you do not need to bring it up unless you feel strongly about it. In fact, as a general rule, do not answer any questions you have not been asked.
I am sure what all steps you have taken to try and find your tickets, but here are the steps I took (in case you haven't tried any of them) to find my ticket:
1. Start by looking up/googling "ecourt + your local state".
2. If #1 is successful, great. If not, just look up "search + pay traffic tickets online + your local state".
3. Once you have found your local court's online tool, do an electronic docket search on their website, maybe even an advanced case search, and run a search based on your names -- if you have more information you can enter, such as a date range, etc., then so do -- hopefully this yields the results you need.
4. Once you have your court case/ticket information, proceed to search your email for a mail receipt of the ticket. A general rule of thumb is to search for the domain (look at the link of the page where you searched your ticket and search for that same domain in your email) name in your email, example: iowacourts. If searching for the domain doesn't work, then search court, or judicial brach in your email(s).
If after all those searches you still cannot find information on your tickets, that is okay. Just plan on providing as much information as you recall when asked.
Good luck on Wednesday, and I will be praying for a positive outcome for you!
