I have the same problem with one of my (two) AppleCD SC drives. I'd like to get it working again. I found these 12 tooth gears on Aliexpress, they are VERY close. 4.3mm OD (vs 4.4), and a bit "taller". Shouldn't be an issue since there seems to be room for it, but I could always sand it down a bit. 2mm bore for the shaft, I'm just hoping it will fit snug (I suppose a bit of glue may work to prevent it from slipping). I just ordered 10 (minimum order available) for only $8.80 shipped. I'll report back with my results. If it doesn't work out, I guess I'll have a parts unit.
https://www.aliexpress.com/item/2251832871970041.html?spm=a2g0o.order_list.0.0.21ef1802eDxoQf
https://www.aliexpress.com/item/2251832871970041.html?spm=a2g0o.order_list.0.0.21ef1802eDxoQf
