Hello, I would like to know if and where I can find a property damage release of liability waiver that my clients can sign on-site. Computer repair.

My advice would be to invest in the help of an attorney to draft up the document for you.  In my experience, while there are some good provisions here and there floating around the internet, they often have holes in them.  The thing is, you may never have an issue where the document will even come into play, but if you get sued by a client, you want to make sure that document is going to hold up in court and protect you from liability.  At least if you have one custom drafted by an attorney, you'll know what it says, what it does, and how it protects you.