Be awarre that new synchro's don't always fix the problem. What is also quite common is that the tapered journal upon which the ring runs can also wear. If they get too worn, a new ring wont fix the problem. Although the gear and the syncho hub is actually two piece, the hub it'self can not be purchased on it's own. Since these boxes were still being sold new up untill 2007, theres a reasonable chance that new gears might still be available. But you might find that they are spendy.
You wont know till you tear it down if the hubs are worn too or not. ONe time I fixed an out of spec box by fitting the ring from fifth gear to 2nd gear. Since the upshift to fifth takes little effort, the ring had the least wear. (As did the hub itself)