Clinical trial registries are helpful for locating trials that haven't been published elsewhere. You can also locate results, protocols and contact information in these registries.
If you are interested in a specific drug or device, it is good practice to also check drug or manufacturer Web sites as well for anything that might be otherwise missed. See the 'Industry Sources' box on this page for more information.
Some information on trials may also be found by checking the manufacturers' Web sites. They can somtimes be difficult to navigate. Searching google for your keywords just in the company's domain may help if you're not having much luck using the site's search box. For GlaxoSmithKline, you might search site:gsk.com along with your keywords.
As an example, here is a link to GlaxoSmithKline's Clinical Study Register. Not all of the studies listed under "Results Summaries" have been published. The summary documents indicate whether the results have been published and, if so, where.
You may also want to consult the International Federation of Pharmaceutical Manufacturers and Associations site. A clinical trials portal is available under "Ethics".