eBay is a good place to try. Or like niterider said, from someone who's done an ear shave and still has the removed parts.
Or, if ya want new, Ron Ayers.com or Bike Bandit.com are popular places to order online.
Just outta curiosity , which side did ya go down on? (it doesn't matter for the filter cover as they are both the same, right or left)
AKA: Tim & 'The Adventure Cycle' VROC #24567, NEVROC, SteelCity VROC
"When life throws you curves,
Aim for the apex."