I'm looking for Michael Haydn's Violin Concerto in Bb major, P53. I heard a recording of it by Baiba Skride. It's terrific and charming. I'm most interested in the violin solo part, but I'd be ecstatic to also see a piano reduction.
Additionally, Joe Haydn's Violin Concerto in A major should also be up on IMSLP. I have a new copy of it which is unfortunately not PD. It's the best Haydn violin concerto albeit the least popular.