The daily number of customers at the World Famous Gold and Silver Pawn Shop depicted on the show has gone from 70 to 5,000.
"It's made production hard because we can't let them all in at one time because it starts to look like a studio show and not a reality show," Montgomery told the Banff World Media Festival.
"We also have to make sure they're not in the way. They all want to take pictures."
History Channel's top-rated show, "Pawn Stars" chronicles the activities at the Las Vegas shop operated by Richard (Old Man) Harrison, his son Rick, grandson Corey (Big Hoss) Harrison — and Corey's childhood friend "Chumlee" Russell.
Montgomery illustrated how popular the stars have become with an anecdote about accompanying the cast through New Orleans' French Quarter during the Super Bowl.
"It's out of control and I said: 'This is a bad idea.' We're walking through with all the guys and they're being mobbed and I looked over to my right and there is Paul McCartney on a little bike and nobody's messing with him," Montgomery said with a chuckle.
"The guys have been very, very smart in how they have turned a great show into a way to build their entire business."
The series depicts the staff's interactions with customers, who bring in artifacts to sell or pawn and haggle over the price.
There's no longer a need to sit and wait for interesting items to come into the shop.
"We now get thousands of submissions of stuff that people want to bring into the shop. So it went from the beginning trying to co-ordinate finding these great items and that took a lot of work by our casting teams. Now it has sort of flipped," Montgomery explained.
The Banff World Media Festival runs through Wednesday.