Where to buy kitchen hood/vent cover to stop cold air

The topic says it all: Where to buy kitchen hood/vent cover to stop cold ai r?
The louvers on the outside/outdoors end of the pipe from our kitchen stove vent hood do not close completely, so we have cold air coming into the area over the stove. Since our furnace and our fireplace both get their combus tion air directly from outside, cutting off the leakage should not cause an y problems and would cut our heating bill a little.
I know I have seen rectagular metal or plastic covers that mount just below /under the filter in the range hood and that use magnets to hold them in pl ace, but I cannot find them in any of our local big-box hardware stores or even on line. This is not one of the fancy hoods, just a plain hood with a 2-speed fan and one incandescent electric light.
Help!?!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 7 Dec 2013 20:42:10 -0800 (PST), " snipped-for-privacy@sbcglobal.net"

If you don't use the fan often in winter, cut a sheet of something and put it under the filter. Then sell the house that way and see how long it take the owners to complain.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 7 Dec 2013 20:42:10 -0800 (PST), " snipped-for-privacy@sbcglobal.net"

If you use the hood fan as little as we do you could just slap a cover over the leaky louvers
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The exhaust goes thru the roof, and with the snow we are having today, I'm not going up on the roof to inspect the louvers. BEsides we do use the fan a few times every week so closing off the outside is not an option,
I do have a piece of thin plastic inserted between the filter and the frame , and it has stopped the leakage for the most part ~95% or so. I was just hoping to find aomething a little more "professional" to do the job. SWMBO likes factory-built things whenever possible, not kluges that I make up, ev en when they do look good.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.