In addition to Ideal's NoAlOx there's also Burndy's Penetrox, GB Electrical's Ox-gard, etc. One's probably as good as another.
If you have a Home Depot or Lowes or other building supply/lumper yard in your area they may have it in th eelectrical section, as should larger better stocked hardware stores, though an electrical supply wholesaler certaintly will, as should MSC (
www.mscdirect.com) W W Grainger (
www.grainger.com) or McMaster-Carr (
www.mcmaster.com) and many other on line hardware vendors.