I have brewed a (M)Oktoberfest that turned out pretty good. I believe you have many options. For instance, you could use California Common yeast which is a true lager yeast that performs well at Ale temps. Another option could be Mangrove Jac's workhorse yeast which they say is lager-like. Another could be K-97 German Ale yeast which produces clean, clear beer such as Kolsch which is a lager-like beer.