You can buy a rear wheel with aluminum rims and stainless spokes here:
http://aebike.com/page.cfm?PageID=30...ils&sku=WE8691
or here:
http://www.bikepartsusa.com/cgi-bin/...=wheel-27_inch
They also have 6-7speed freewheels:
http://www.bikepartsusa.com/cgi-bin/...?item=01-94974
If your current rims are steel, change the wront wheel as well.