trying second display to a Early 2008 20 inch iMac and can't locate an MINI DVI adaptor

I'd like to add an additional display to my early 2008 20 inch iMac. Apparently Apple is no longer supporting the older iMacs and I'm having the devil's own time locating "how to info". What Iv'e been able to scrape up I believe a MINI-DVI to VGA adaptor would be a simple solution. Unfortunately all I seem to be able to locate are Mini display to VGA. Any suggestion where to source the former or possibly a work around?

Thanks Greg