Having grown up on the Niagara frontier, I ate plenty of beef on weck.
Several restaurants in Niagara Falls (not just Buffalo) served this tasty
sandwich. One restaurant that served it, if I remember correctly, was called
Zwickelbauer's Hofbrau and it was on Niagara Falls Boulevard (Rt. 66).

You might like to know that the sandwich has come east as well. A restaurant
in Albany, The Chambers, used to serve it (they flew in the "wecks"
everyday). Now a drive-in restaurant in Saratoga Springs, PJ's, serves "beef
on weck" during the summer (PJ's moves to Sarasota in the winter and I assume
they serve "wecks" there also). PJ's also carries on another western NY
tradition by serving loganberry soda (excuse me, that should be "pop") with
the beef on weck. You can buy the '"weck" at DiCamillo's bakery in the
"Falls," if you are ever there.

Jim Corsaro