Here is a list of publications that accept manuscripts from Mathematics & Statistics and their related fields. You may also want to search the General publications list.
The Developing Economist
Publishes outstanding undergraduate research in the fields of Economics, Mathematics, Political Economy, Finance, and Public Policy
SIAM Undergraduate Research Online
A web-based publication devoted to undergraduate research in applied and computational mathematics.
Involve: A Journal of Mathematics
Involve showcases and encourages high-quality mathematical research involving students from all academic levels.
The Journal of Young Investigators
A student-led initiative to broaden the undergraduate scientific experience, allowing students to participate in the scientific review and publication processes of its peer-reviewed undergraduate journal.
Missouri Journal of Mathematical Sciences
Publishes well-motivated original research articles as well as expository and survey articles of exceptional quality in mathematical sciences.
Rose-Hulman Undergraduate Mathematics Journal
Devoted entirely to papers written by undergraduates on topics related to the mathematical sciences.
Undergraduate Journal of Mathematical Modeling: One + Two
Concerned with various applications of mathematics done by non-mathematics majors. In particular, its purpose is to disseminate selected applied mathematics projects of engineering and science students.