For what it's worth, where we are, the teachers are not permitted to continue the DRA test past the end of one grade level above the student's current grade level - that's a pretty low ceiling. In other words, for a gifted kid, it's not likely to be an accurate reflection of reading level.
How necessary is it that you have an "accurate" DRA score? What would you do with it? For advocacy purposes, I'd probably look for one-on-one achievement testing rather than re-doing DRA without the ceiling.
Perhaps one of the local tutoring centers (Sylvan, Kumon, etc.) would be able to give a DRA test.