I'm not sure which type of gate to use, but I know there are a lot of different gates out there now, for all kinds of different situations. Try looking at Babies 'R Us, at babyage.com, and googling "baby gates" or "safety first" to see what you can find.
I do have an idea for your metal bars. You could use plexiglass/thick plastic to cover the whole area, drilling holes and using something (zip ties?) to attach it to the bars. If you can't find that, then even something like thin plywood or wainscotting would work. It's relatively inexpensive, you can drill holes in it easily, and you can cut it to whatever size you need. It wouldn't have to be really thick, just strong enough that your kid couldn't break it. If none of that will work for you, maybe you could use some strong fabric (like canvas type) to cover it, and sew some strong velcro or ties to the ends and tops to keep it in place. It would have to be very taut to work, but if the other options aren't a possibility for you it would be better than nothing. I wonder if Babies 'R Us or someplace else has plastic sheets that are made for this? They're coming up with new stuff all the time! In the meantime, you could always use some stiff cardboard and good old duct tape!
Good luck! Hope this helps!