I was checking Wikipedia's list of organ concertos, and a composer by the name of "Skitner" is listed there as having written one before 1802.
https://en.wikipedia.org/wiki/Organ_concerto#Skitner
Now, I have no idea who this mystery composer is. I've tried searching his name, but it constantly links back to the same pages. We only know he was a "Central-European" composer. Maybe someone on this forum knows more about this one? If it turns out this composer is not within our remit the thread could be closed again.
Here are the details (in German) from the Landesbibliothek Coburg where the score of an Organ Concerto in D is held; unfortunately no further information is given about the composer:
Signatur/Buchnr.: Ms Mus 374/1.52
Verfasser: Skitner, ...
Titel: Concerto in D
Einheitssacht.: Konzerte, Org Orch, D-Dur
Untertitel: Organo Principale, Violino Primo, Violino Secundo, Clarinetto Primo, Clarinetto Secundo, Cornu Primo, Cornu Secundo et Tympano
Ausgabe: [Stimmen]
Verlagsort: [S.l.]
Verlagsort: ¬$a [S.l.] ¬$c [um 1825]
Jahr: [um 1825]
Umfang: 8 St.
Allg. Fussnoten: Handschriftl. - Komponist nach RISM. - RISM 450107181
Erstsignatur: Ms Mus 374/1.52
Zweitsign.: Mus Ms Mus 374/1.52
Lok. Schlagwort: Skitner, ... - Stimmen. - Musikalie
Verbund-ID: BV040303056
Alias of one of the Kistner family publishing house (eg father of Karl Friedrich Kistner)?
An interesting thought. Have you any evidence?