found some vents that mount on the side of faring and they open to

For the motorcycle in your avatar? You need one for that?
http://www.ceebaileys.com/harley/index.html

I reckon a windscreen store could help you out...Harley Screen are perspex...so they know how to cut em BMW make vents for screen i bet you could adapt one.

thanks for the info i will give them a try .i know they have some wind shield that are curved but haven' herd how they worked

I'm still curious. Is it for the bike in your avatar?

Perhaps your talking about the Klockwerks?  They make curved shields for the batwing fairing but that doesnt do what you want.  Having a batwing faring Im not sure there is such thing as a vented windshield.  Not that I have heard of anyways....

 For a Road King there's the new windsheild on page 309 of HD P&A catalog.