Probably isn’t going to be easy to track down. The only thing I’ve been able to find is this. The only things that match up are the last name and the timeframe (and even the timeframe isn’t perfect. September 19, 2009.) No idea beyond that whether that’s the “correct” Webber couple. (Also, the wedding registry page doesn’t mention whether Megan took the Webber last name. If not, and if the t-shirt is related, I’d think the t-shirt would use the term “Webber/Lange Wedding” or some such rather than just “Webber Wedding”. But who knows.)

I checked the Wayback Machine hoping an older version of the same page a) might be available and b) might have more information than the basically no information that the current version of that page has, but unfortunately they don’t appear to have any versions of that page saved.

The source of the page doesn’t have much information (aside from what’s visible in the page, the URL, or the title of the page) except for a zip code: 90049. Probably where Megan and Thomas live.

Again, no idea if that specific Megan and Thomas are related to the t-shirt. But I guess there’s a small chance.

Edit: I guess you could contact screen printing companies in LA near that 90049 zip code and see if you can find a screen printing company that will admit to having made that shirt. They might be able to tell you the story of it. If there’s a tag in the shirt, it might even say the name of the screen printing company.