[Techman]

You might be lucky and find someone with spares, but folk tend to have complete decks going spare, so making the part would be the way to go.

It's sprung steel, so it presses against the adjusting screw and follows its adjustment in and out. Ideally, if you make a replacement you'd need to 'temper' it to give it 'spring', but in practice I think you'll get away with an ordinary bit of un-sprung tin so long as you bend it to tension against the end of the adjusting screw and try to keep all your adjustments carefully made in one direction only, as it won't want to follow the screw back out again if you go too far. So to sum up - I think you can fairly easily make the part.

One last observation - it's a very clean deck from what I can see (less dusty than mine), so someone's given it a going over. It makes me wonder why someone needed to dismantle the arm far enough to lose that part and also makes me wonder whether there's any other lost or misassembled parts on the rest of the deck, hopefully not.