The dual forms طَالِبَانِ and طَالِبَيْنِ both end in nūn, normally with kasra.
This nūn is not tanwīn; compare the singular طَالِبٌ.
Additional rule: In iḍāfa, the nūn of the dual is dropped, e.g. طَالِبَا الْعِلْمِ and طَالِبَيِ الْعِلْمِ. The detailed treatment belongs to a later topic.