What year is the bike? Different years use different size wheels. Depends if you want to go stock or not. Stock wheels can be found, they are usually pretty rusty and take work to fix, and run from $50-200 each. New spokes can be had from Wayne Mahaffey, around $40 per wheel. Having rims blasted and powder coated run around $100-125 per wheel. A front brake setup is another $300 or so. Put this all together and it gets expensive fast but looks great when done. Look at the photos below for a pair I did recently.
If you want to adapt something, look at Worksman wheels. These are really well built, heavy duty bike wheels that approach motorcycle wheels. They can be had with a front drum brake for about $100 and look pretty decent. Check the replica bike in the last photo of a worksman wheel with drum brake.