I think people might be a bit reluctant to assist with this request simply because it possibly involves "helping to hide the evidence," even if your request says the opposite.
In other words, imagine someone under investigation for embezzling money asked you to help them locate all the financial records they had deleted, the same ones the FBI is currently searching for. Is it possible they turned over a new leaf and want to help the FBI arrest them? Sure, it's possible. But history would demonstrate that most people who hid evidence in a crime would rather it stay hidden.
The situation is similar here. If you want to know how your ex found out, ask him, and if you want this info in order to help "do the work" then that is something he should be aware of. Most BS's practically have to beg their WS's to make an effort to do the work, so good on you for making the effort! However, post-affair, things get messy. Most BS would tell you, "You certainly made an effort to figure out how to hide the info, so make the same effort in retrieving it."
You have the same ability that we do to jump on Google and search for applications and services that will help to restore deleted texts, there are many options.
One reason to reach out to your BS is simply this: By asking for their input, you are giving them back what you took away from them during the affair, which is their CHOICE, their agency, and their ability to say what they do and don't want. Your spouse may say to you, "Thanks, it would be helpful for me to see those lost messages, here is how I found the info when I looked...". Or, they might say, "I don't give a damn if you find the messages or not, it changes nothing, and I don't understand what you hope to accomplish". No matter what their response, it makes it clear to them that you are making an effort. If you don't make them aware, then you are hiding information from them. Again.
By making the effort, and NOT making them aware of it, you are (whether you intend to or not) hiding your actions and intentions from them, which is what you did during the affair, so when/if you are found to be secretly be looking for evidence, whether you find it to not, your BS will recognize the secrecy, and see it as manipulation once again. I doubt that's your intended outcome.
Honesty and transparency are the best policies after D-day. As a WS, it can be very scary to open up lines of communication and truth, because it runs the risk of bringing up more anger and more pain, and in many cases, we are already in a bad enough predicament, and don't want to add gasoline to the fire. But the truth is, until it's all on the table, nothing can be resolved. And until you, the WS, can truly "own" what happened, nothing can be resolved. And doing that takes time. It takes effort. It takes a lot of courage and a willingness to throw yourself under the bus when necessary, because no one wants to forgive someone who can't even take ownership of what they did wrong.
I see your signature says you joined very recently, this month, in fact. I'm sorry things are so hard for you, for both of you. Infidelity is a real shit-show, and most WS's don't actually comprehend what it takes to recover. Our experience is that it takes 2-5 years for most couples to "recover", and by recover, I just mean "getting to a point where it doesn't absorb every second of every day" and where R can even be attempted. It's important to understand this. There is nothing you can do or say right now to "make everything better." It's like healing from a broken knee cap - healing takes time, and no amount of money or doctors can speed that process up. Similarly, infidelity has a slow healing time. It is a game of progress, not perfection.
I just want to finish with his. My advice might sound a little harsh, and I apologize for that. It's not meant to be harsh; rather, it's just raw honesty. The people here, myself included, made the same mistakes you did, we also panicked and did all we could to make it go away, and we made many mistakes along the way. So our advice often comes from a place of "knowing you need to touch the hot stove to see that it's really hot", but having already confirmed it's hot ourselves, we may urge you to take more productive steps instead.
I really applaud that you are here looking for support and making the effort to make things right. You came to the right place for help. The truth is, most (90%+?) WS's never even make the attempt to make things better, so you are already ahead of most people, and that's something positive to hold on to for now. You can't fix things without making an effort, and you are already making an effort, so good on you. Stick around, we'll try to help you focus your efforts in whatever ways we can.
Good luck to you both.