You can get the factory keyless entry system from Bavarian Autosport for around $371. It's not free, but mine's worked great for 13 years and the install is exceedingly easy. There used to be a retrofit kit for the OBC but I don't think it's available anymore. I'm not sure what use the OBC for but you might consider a ScanGauge. It's much cheaper and actually gives you a lot more information out of the ECU. Best part is that you can change the screen color to match the stock lighting and it fits nicely in the tray in front of the ashtray.
www.scangauge.com