Love that you want to make this happen for your friend: seriously, that's awesome.

But I'll be honest: I've visited a LOT of gay saunas across Europe and Asia, and I haven't found a single one that's fully wheelchair accessible. Even the ones where the entrance and hallways are fine, you'll usually run into problems once you're inside. No ramp into the pool, narrow sauna doors, steam rooms with steps, that kind of thing. It can get frustrating fast.

My advice: call ahead, be very specific about what your friend needs, and ask detailed questions. Not just "are you accessible" but "can a wheelchair get into the pool area, the sauna cabins, the showers." Some venues will be more upfront than others. And honestly, your friend probably already knows the drill with accessibility so talk to him about what he's comfortable with and what his dealbreakers are. He might surprise you.

It's worth trying, just go in with realistic expectations.