A queen excluder is not typically part of a top bar hive, because they are operated under totally different principals compared to typical box hives (langstroth, national etc...).
In a Langstroth:
The beekeeper harvests whole boxes of frames at once. They don't want brood in any of those honey frames, so the queen excluder is used to keep the queen in the lower boxes, while the workers fill and cap the honey frames above.
In a top bar hive:
the beekeeper harvests bar-by-bar. You lift a bar, look at it, and decide if it is ready to harvest. If it has brood it is returned and left for another time. During harvesting the whole comb is cut from the bar, before being returned to the
bees. There is no need for a queen excluder in such a system.