Going through the main page, I came across some interesting articles, including a work list of Chopin. Although it's mentioned that the work list contains more works than most other lists, I could find 2 (or 1) work(s) that are not on the list, but are certainly written by Chopin.
I think those are these:
Krakowiak: Grand Concert Rondo op. 14
for pianoforte & orchestra in F Major
Op. 14 (Br. 29) composed 1828/11-12
A Krakowiak is a Polish dance in 2/4 time of the Krakow district.
dedicated to la Comtesse Anna Czartoryska Sapiehow
The Grand polonaise in the version for Piano and Orchestra, op. 22
(This is discussable, because the original piano version is mentioned and most people see it as the same).
I hope it's true