You can look for the route GPX from the event’s web site. Then you can check some other map portals, like Suunto’s Movescount, http://www.gpsies.com, mapmyrun etc. Usually the routes tend to stay the same, and somebody has perhaps ran the event in the past and made the workout or route publicly available.
If still no luck, you can do it all by yourself in some of the route plotter portals. Our favourite is http://www.gpsies.com. It is easy to use and there is no need to register, just plot the route and export to GPX and you’re done! Usually the race events have at least some route map available, so just plot the route based on that map.
There is a little work involved in this part of the process, but we try to keep the readymade list populated. We are soon opening a portal, where users can add races to the list, to save time from other participants.