Best of luck, OP. Stay patient and engaged, and the right one will come up. It took me almost 1.5 years to find mine, but I was stuck on only one color. If you are ok with white or black, you'll find one much sooner!
EDIT: forgot to mention that the E90 M3 is not really a long trip car, unless you mean two-lane twisties!
The 6MT needs a seventh gear it does not have to bring back the revs - it never loafs comfortably like an E39 M5, or gives you that highway middle-tach sewing machine smoothness of an E46 ZHP. No, the E90 growls and asks for you to push. I recommend trying one out on the freeway at your desired cruise velocity before buying.