Here is a link to the trial version:
This is the trial version, but it can be activated with your existing serial number. If you don't have your serial number, but you registered your Lightroom with Adobe then you can log into your account get your serial number. If you didn't register your software, and you don't have a record of your serial number then you will have to contact Adobe. Serial numbers are crucial, and care should be taken to ensure that you have access to them for situations such as the one you are in.
Thank you very much!