Sorry to arrive to this discussion.
Just a few ideas from an old dog.
I think that the exhibitions are great, but their "market" (shoe repairers) is shrinking. Why not give it a different name and open and advertise, the exhibition to the public?
Attract and invite new related exhibitors, such as high end (repairable) footwear manufacturers. Shoe care bloggers, who can also promote the exhibition online.
Work out why repairers dno't attend. Is it too far? Is it too expensive? Perhaps a questionaire through wholesalers.
As I said just a few ideas, trying to be positive