As you can see from my signature I'm not running a dive shop any more. Go into Island Divers and ask for Rudy. He keeps octo holders in the retail shop.
I believe (though I haven't been able to confirm) that "Junior" at Ecologic is a Genesis technician, but I'm quite sure that the only spares he'll have (if any) will be service kits. He won't have any body parts. Actually, thinking about it I did do the Genesis technician course a few years ago but I've never worked on one since.
I don't really understand your last comment. If as I believe it's just a blanking plug its absence shouldn't have any effect on the operation of the octo. Have you tried it? - I should.
It's always best to ask advice before trying to modify a second stage - or indeed any other scuba gear. On some the hose can be switched to the other side easily, on others it's possible but a major dismantling and reassembly/readjustment job requiring special equipment and knowledge of how to use it, and on most it's not possible at all. You can't tell by an uninformed inspection - for example, most Scubapro second stages (for which I am a technician) cannot be reversed, though they look much the same as the few which can be. I don't know whether that particular second stage can be reversed.
I don't know who you're diving with, but the best times to see Rudy are early in the morning (8-8:30am), at lunch time (12:30-2pm), or later on (c. 4:30-5pm). I know he's teaching a course tomorrow, so outside those times will be difficult. Both the dive shop and his retail shop are manned all day though.