Beethoven scholarship has revealed quite a few pieces for piano and orchestra beyond the usual five concerti. I have most of them (in various formats: orchestral, sketches, completion, midi).
(1) Piano Concerto in Eb, WoO 4 (1784) 27' - piano score survives, orchestration completed by Hess.
(2) Andante in D (1788 or 1792-3), intended for Piano Concerto in A, Biamonti 55, 9'34 - fragment (broadcast on NPR)
(3) Rondo in Bb, WoO 6 (1794-5), 9'29 finale, possibly to Op. 19 concerto.
(4) March with variations in Ab (1802) 2'27 (unfinished sketch)
(5) Piano Concerto in D, Op. 61 (1807) 46'00 (transcribed by Beethoven from Violin Concerto)
(6) Piano Concerto in D (1815) 16'00 (performing version) Hess 15. I have two scholarly articles about the extent of Beethoven's sketches for this, including illustrations of the sketches. In my opinion, the exposition (orchestral and solo) is pure Beethoven, it gets fragmented further in the development.
(7??) Piano Concerto in D (first movement - Allegro) (WoO Anh. 7) 14'37 (1788-1793??). Possibly spurious but interesting, nonetheless.
Cheers,
Balapoel