Ive always been able to go down to my local Napa and give them the year/make/model of my car and the had the right one for me. Just be sure to get a good rubber gasket and not a cork gasket. As for install make sure both surfaces are clean and dry and that the valve cover has not been overtightened in the past and warped around the bolt holes. You dont need the bolts to be super tight, just nicely snug.
Also, nice thing about the rubber gasket is it can be reused if you have to take the valvecover back off in the future.