There generally aren’t DSLRs made with unusually large physical controls specifically for this need. The most practical options are remote-control solutions.

If the camera can be set up in advance and used mostly like a point-and-shoot, many DSLRs support a cable release for firing the shutter. That works well for a wheelchair/tripod-mounted setup, though changing settings on-camera may still be difficult.

For more control, tethering can help: some cameras can be controlled from a computer, and in some cases from a phone or tablet app. This can make focusing, changing settings, and releasing the shutter much easier, especially if paired with accessibility features on the computer or mobile device.

If manual exposure control is important, an older or manual lens with a physical aperture ring may help, since it provides a larger control surface than tiny camera buttons. Compatibility varies by camera and lens, so it should be checked before buying.

So the best answer is usually not a “large-control DSLR,” but a camera that supports cable release, tethered shooting, or mobile remote control.