Many parts are still available for your old drive. To buy an old drive, you can check e-bay, advertise here on the forum, or buy an older boat used and resell it with the newer drive. You also have to know what you're buying. For instance, there are aluminum as well as plastic frames with stainless sprockets. Condition is important. You can also convert your new drive to stainless sprockets. The conversion requires several parts though, like bushings, sprocket guards and cotter pins.
Any overly cautious use on the newer Drives is, IMO, is a disservice to yourself. The new drives have had some problems, but they haven't been that common. There are a couple of areas where they are superior to the older drives, like solving the chain skipping issue. If your new drive is still under warranty, you're much better off using it if there is a choice -- if there are any problems, you can get them fixed under warranty!
My new drive has been excellent lately. I use the Turbo fins 22 to 28 miles per week and push them hard -- sprints, boat wakes, etc, they get no concessions! The Drive, adjusted and lubed, runs just as smoothly as the old ones -- like soft butter. Most importantly, it gets inspected after each outing; problems are pretty easy to spot before they happen in most cases (once you know what to look for). Mast mounts for your fins and adjustment holes on your drums typically show wear well ahead of any failure. That's the best time to address the problems. Truly spontaneously failures can happen, but they are pretty rare.
Check the kayak FAQ section here for more maintenance / adjustment info:
http://www.hobiecat.com/community/viewforum.php?f=21