I don't know about bedrails at AoA but if your son isn't a sleep all over the bed child, you could do the pool noodle trick.
Bring 2 pool noodles (once I brought 4 for my Daughter who was a roll all over the bed sleeper) - I used to put them around the edges of the inside of my luggage before I packed.
Then when you get to the resort, I'd put them under the bottom sheets, one on each side (2 on each side for my Daughter) and I'd tuck the sheet around it a little bit.
They were just enough to stop him from rolling off the bed at night.
Those pool noodles were great backups when we didn't arrive at the resorts until late at night and the bed rails were all given out already.