You can also try 
www.ChoppersUS.com or
see below links for more info
Ebay.com - Buy & Sale Schwinn & Sting-Ray Bikes & Parts
eBay is The World's Best and Biggest Online Market Place.
( 
schwinn | eBay )
J&B Importers - 
http://www.jbimporters.com
IBD Sales for OCC Schwinn Sting-Ray parts & accessories.
http://www.jbimporters.com/nondealer/search.phtml?search_text=stingray
Schwinn Japan's Web Site - 
SCHWINN ƒVƒ…ƒEƒBƒ“
http://schwinn-jpn.com/05bikes/stingray.htm
Some Schwinn & Sting-Ray Information Sources can also be
found at the Independent Schwinn & Sting-Ray Yahoo! Groups.
( 
Schwinn-StingRay : Schwinn-StingRay Enthusiasts Yahoo Group )
"Oh heck with" here's one of my Schwinn Stingray Secret Parts online store!
You can purchase a complete Schwinn Stingray Chopper rear wheel for $20.00 less the tube & tire which are sold separately, see the Link below.
Bargain Basement Bicycle Parts - Catalog
Wheels Rear
WR54	20 x 4" StingRay rear wheel steel/alloy 36H black/black/silver	$20.00 New!
WR55	20 x 4" StingRay rear wheel steel/alloy 36H black/red/red	       $20.00 New!
WR57	20 x 4" StingRay rear wheel steel/alloy 36H black/black/green	$20.00 New!
WR58	20 x 4" StingRay rear wheel steel/alloy 36H silver/silver/black/	$20.00 New! 
Let us know when you find a replacement, you know that rear axle is 170mm, it'll be cheaper to just order the wheel from Bargain Basement Bicycle Parts and $20.00 ain't a bad price for the complete new wheel I will say.
C.H.