As Greywater said above, you can't buy just the arm from the factory, but you may be able to get it a an RV salvage yard.
You also may be able to get the bent one fixed by straightening it and having some stiffeners added to it. It'll be easier to pull the whole assembly and fix it while assembled than to try to take an arm off.
If you do want to remove that arm, you have to disconnect the lead screw in the middle and remove the holding plate at the end. You may even have to remove the motor if the bent arm is on that side. The trick then is to 'sync' both sides when you put it back together.
Here's a link to the service manual for them. Lippert Electric Rear Stabilizer Jack Service Manual