My suggestion is to look for developers on various job boards and also check out the development firms.
FileMaker has a job board, as well as http://www.findfilemakerdevelopers.com/
Making a pretty UI should never sacrafice functionality IMHO so its important to see samples. BTW, designing for Windows users is different when it comes to the UI because of the flashing issues. It is a lot more noticible when using large background images or header images etc so it can be limiting.