Also find info at Kubota.com under previous products tabs.
Production 2004 thru 2007?
One thing to realize is that while the tractor number may change, it may not represent a radical change. In other words, it may be that many model numbers are essentially the same tractor. I would not be too concerned. The tractor you look at needs to be judged on its own merits.
The 7610 was current up until a few years ago. Like BP stated, there were several model numbers to signify very small changes. That series of tractors goes back to at least the early or mid nineties..... maybe earlier? You should have no problem finding parts and accessories for that tractor for a long, long time.