My Husqvarna zero turn was built in 2002. It runs fine but the deck is very loud. I was told I need new spindles but they aren't available. Not being a mechanic, I was wondering if the bearings could be the issue and if so can they be replaced without damaging the spindles and would those bearings even be avaiable. 

Remove or at least loosen the deck belt.  Then spin the spindles and idlers feeling for
any roughness / noise.  ANY roughness, they need replacement.
 
 
Now, it seems the bearings inside the spindles are available, part #27:
 
https://www.partstree.com/models/zthkw-4218-968999167-husqvarna-42-zero-turn-mower-kawasaki-2000-05/42-deck-assembly-0/
 
There should be a bearing part # on the bearing(s) themselves. Get that # and
do a search.
You should be able to get the same bearings much cheaper ($ ) than the OEM'S 
 
Definitly repairable..
 
.