Why not just contact them and ask them what plugin(s) they used or have them put you in touch with their developer?
I guess if nobody recognizes it I will have to. What incentive does the developer have to share that information with me. If it is somebody who does it for a living, which it most likely is, I would expect them to say “get me to do your website and I will use it for you”
If someone contacts me about one of my websites or one I developed and has anything positive to say, I’m absolutely thrilled. I’d be happy to tell them how I did it. Yes, it’s a sales opportunity, but it’s also someone noticing my work in a validating way. Make someone’s day! Tell them they did a good job.
Ok, I will give it a try.
I guess my other thought is that I am first contacting the company who has the website. They might just ignore me if it is not related to a sale on their end. But I gave it a shot