Welcome to TE! I can't get you anything specific (since I'm only an embryonic runner...), but a duathlon training plan is exactly what you need. (Biathlon is really cross-country skiing and target shooting. People mix them up all the time, which is why Google looks up duathlon training plans instead. )

When's your race? Can you already do the target distance on the bike? If you can do a half-marathon, I think you can do this without too much trouble. What they call "brick" workouts (bike and run back-to-back) will be your friend. Incorporate that into your training, and work up to something close to the distances of your race. There are plenty of existing training plans out there--find one that works for you and tweak it if you need to.