If they were catching 2-3 Tigers on a stream per trip, someone was putting stocked Tigers in that stream. They just don't occur in that kind of frequency naturally in the wild, even under ideal circumstances with a healthy mixed wild population of Brooks and Browns.
There's some clubs in PA that still stock Tigers in places. If it's just your objective to catch a Tiger, and not necessarily a wild one, try to research where that happens and fish there after they stock them. They shouldn't be all that difficult to catch.
For a wild Tiger, it really is just plain dumb luck. Just fish whatever is working best for the conditions of day and time of year. That may be a straemer, a hatch match situation, or an attractor type of deal...depends on the conditions. If it happens, it happens. If not, you just have fun catching wild Brooks and Browns. There really is no recipe for success for catching one. Cast a fly likely to be eaten, to a place likely to hold a fish, on a stream that's most (relatively speaking) likely to produce a Tiger. That's all you can do.