Hi Elizabeth - what style etc., Although I love Marches this is not one that I have personally played before until your request, although I do know the melody.
The Organ March in the Organist style on the KN7 slowed down to around 100 or so is not a bad place to start and with a little tweaking should be quite reasonable to start with.
Unless you have some commercial styles or can tweak your own then the Marches in the March & Waltz section are limited.
Bill Norrie who has offered his help I am sure will do an excellent job for you.
Anyway - Have a go - good luck.....Joan