https://www.amazon.com/Ibanez-2LE21B-Tremolo-Arm-Black/dp/B004L66AM6/ref=cm_cr_srp_d_product_top?ie=UTF8 This one might fit, according to the seller and according to Rich in this Jemsite thread: https://www.jemsite.com/threads/replacement-trem-arm-for-powerocker-ibanez-rr250-rebuild.158721/

If, like on most trem systems, the arm socket is removable, you can also see if you can just remove the socket and put a different one in (cheapest option would be from a Floyd Rose).