It is a Three-Barrel Gun Co. folder/broadside of probably 1907 vintage. The earlier, circa 1906, Three-Barrel Gun Co. catalog only has the three-barrel gun in it but has on the bottom half of the back page --
"DOUBLE BARRELS
While we do not carry double-barrel guns in stock, we will be pleased at any time to build them to special order, when sufficient time is allowed, either with or without Automatic Ejector.
Our Double Gun is the strongest and simplest constructed gun on the market, and for those who do not care for the advantage of the rifle barrel, a better gun could not be found."
The flyer/broadside that Daryl pictured includes their Lefeverish single barrel trap gun, but I see no mention of doubles on my copy of that broadside or in the 1908 Three-Barrel Gun Co. catalog.
The Royal Gun Co. catalog only covers the three-barrel guns and the single barrel trap guns, but often includes a separate folder on their double guns, which were in a separate serial number sequence.
From Rudy's copy of the old Three-barrel and Royal Gun Co. ledger it appears that the Hollenbeck Gun Co. doubles were serial numbered right along with the three-barrel guns as a handful of them remained in inventory when Three-Barrel Gun Co. started the ledger.
