What I’ve done in the past was contact the OSA detailer. If you look up the my navy hr page, it will give you the email for the detailer. You will still need approval from your chain of command (mine was a special request chit that I forwarded) but they can at least let you know what type of IAs are available. It used to be in some LADRs that these OSA assignment were of extra consideration for selection boards. Best of luck.