Answer
Lobby Data Sources can't reference an IAL directly this way — the workaround is to add one extra layer of indirection: create a Quick Information Source (QIS) that uses the IAL as its source, and then build the Lobby Data Source against the QIS's own generated view instead of trying to reference the IAL directly. This extra step resolves the 'unable to find' error, since the Lobby Data Source mechanism can consume a QIS view where it can't consume a raw IAL.