Get the unique constraint columns list (in TSQL)?

Ed is correct, the columns are exposed on the constraint column usage view, here is the SQL for it.

select TC.Constraint_Name, CC.Column_Name from information_schema.table_constraints TC
inner join information_schema.constraint_column_usage CC on TC.Constraint_Name = CC.Constraint_Name
where TC.constraint_type="Unique"
order by TC.Constraint_Name