There's loads of options. From Anbernic to Powkiddy
And there's also older models and types for sale. Check out Retro Game Corps on YouTube for honest reviews, costum firmware and information on these devices.
There's also !sbcgaming@retrolemmy.com but like many niche communities it's not very active. But I'm sure you can get answers for any question you post there.
Edit: there's also options to buy a pre-built retropi or make your own using a 3d printer and a raspberrypi or similar, and costum pcbs. But I'm not sure if that's what you're looking for.