I broke a spindle on my riding lawn mower when I hit a high piece of wood. In any case, I was able to find a matching spindle on Amazon. Pictures online make it look like your mowing deck is very similar to mine although yours is more heavy duty.
There are several similar spindles, but from what I could tell, spindles are pretty universal and the same one will work on many brands. I'd look there and order one that has free returns just in case it's not quite the right one. You could also order multiple ones and return the ones that you don't need.