Your best way to search on craigslist will most likely be to just search "wrangler wheels" or "wrangler rims". You'll have to look at them on an item by item basis to determine the backspacing and may even have to contact the seller, as the backspacing is not always listed in the ads. 4.5" is fairly common in aftermarket wheels, so you should be able to find them fairly easily. You will also need to check and make sure that the wheels are not for a JK wrangler (2007 and up) because the bolt pattern is different. Yours Jeep has 5 x 4.5" bolt pattern.
The backspacing will not effect your tire fitment. For that you will want to get the tire width. 8" and 10" wide wheels are fairly standard and should fit both your 31" tires and 33" tires, assuming they are common sizes. In order to tell you for sure, I would need to know the width of the tires.
Now, my one concern is the 4.5 or 5" of backspacing. Backspacing measures the distance from the mounting surface of the wheel to the back of the wheel. So, the larger the back spacing the more "tucked" in closer to the frame your wheel and tires are going to be. Because of this, I would avoid the 5" backspacing and maybe search for more of a 4" or 4.5" backspacing. Since 33" tires are almost always wider than 31" tires, you want to make sure that you have enough room for the tires to clear the frame rails when your going around a sharp turn.
You probably already know this, but I figured I'd mention it just in case. If your looking to get this done on the cheap, I would look for a 15" diameter wheel. 15" wheels and tires are almost always cheaper than 16"+.
Hope this info helps.