dude hasnt spawned in a minimum of 36 hours, whats the spawn timer?
4 hours
The Mad Merchant can be found in The Wonderworks Toy Shop in Dalaran. He is on a very random spawn timer, reportedly as short as 4 hours, and as long as a few days! Once someone purchases from him (after he has spawned), he will stick around for roughly 1-2 hours before despawning again.
Try searching the group finder. People used to list groups for when he spawned, while a very small chance, it is possible they still might.
Every 37 hours.