Motorized Wheel Chair Source

Any mower will do.
There is 2 ways of doing this.
First is to take a riding lawn mower and remove the engine and axle. Replace the axle with an electric transaxle (These are quite common these day), look for one that is minimum 1000 to 1200 watts. You will need a motor controller for this and throttle (There are foot pedal throttles.), make sure the controller has a reverse function on it. Then you will need a motor (At least 1hp to run the blades - single blde of 36", 2hp for multiple blades)

or, use a lawn mower that has a hydrualic transaxle (very common these days) on it. This way you don't have to purchase a new axle and controller. With this you will need at least a 3hp DC motor that runs at 3500-3700rpm.

Most mowers now use a belt system to transfer power from the motor to the axle and blades.

Now batteries.....this is where it gets expensive. It needs batteries that have a high amp output(Discharge rate), with a high aH (Amp Hour)..and if you use a 24, 36 or 48DC motor, these can range from $300 to $1000 each. (i.e. golf cart batteries which are generally 6 volts). Or you can go for some exoctic battery packs, but these can run $1200 - $3000.

This is why the major manufactuers like Deere don't have any models really to speak of. It's not the cost of manufacturing the battery riding mower, which is about the same as a gas mower, but it is the cost of the batteries. (Say a $1400 riding gas mower, would be about $3500 - $4500 as a battery mower.)

There are some great sites out there for batteries and motors. You can search under "EV", electric vehichle supplies.

By the way, I am making a riding battery lawn mower for myself right now for my 2 acres.