I wish I had some useful information for you. Which armrests are movable seems to be top secret information!
Since the plane has more than 30 seats, it probably does have some movable aisle armrests. Here is the pertinent portion of the Air Carrier Access Act:
§ 382.21 Aircraft accessibility.
(a) The following requirements apply to new aircraft operated under 14 CFR part 121 and ordered by the carrier after April 5, 1990 or delivered to the carrier after April 5, 1992:
(1)
(i) Aircraft with 30 or more passenger seats on which passenger aisle seats have armrests shall have movable aisle armrests on at least one-half of passenger aisle seats.
(ii) Such armrests are not required to be provided on aisle seats on which a movable armrest is not feasible or aisle seats which a passenger with a mobility impairment is precluded from using by an FAA safety rule.
(iii) For aircraft equipped with movable aisle armrests as required by this paragraph, carriers shall configure cabins, or establish administrative systems, to ensure that individuals with mobility impairments or other persons with disabilities can readily obtain seating in rows with movable aisle armrests.
I would suggest asking again, multiple times if necessary.