I need a spindle stem for my Akai reel to reel model 1730DSS

You might be able to find a parts machine on eBay.
If the reel does go onto the spindle but the part that you pull and turn to hold it in place is broken you have two options.
1. Use the machine horizontally so gravity is on your side.
2. Some machines used rubber reel caps to hold the reel in place. A thick disc of rubber with the right size hole will work. You can make one with a bit of trial and error.
If you can't get the reel on at all then you have nothing to lose by trying to straighten it enough to at least get the reel on.