Against the law??? That dumb! Here's 3 ideas.
I replaced a Sears opener several years ago and kept the remote control (no, I don't know why). Post the part number you are looking for - we might have a match. If so, it's yours. If not, maybe someone else here has a spare.
I saw a "universal" key chain remote for garage openers at Wal-mart some time back. It was made by Stanley (or Genie) and was sold as a "universal" spare. Might be a solution for you.
I think what Tshakeel is talking about is a battery operated transmitter packaged with an AC receiver. They go for about $20. I use one for the Christmas tree. It would be a solution but might need a little wiring up or a 110v relay added to adapt it to your door. Mine only has a range of about 25 feet but it would sure be cheaper than a new opener.