Sorry to hear that,But you will have to replace the whole thing.Here what it looks like.Hope this helps.
Attachment 3051
27.90$ on ebay
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Also try this place
www.truckandcarshop.com
Go to the bottom of the page and find the corvette catalog and go to page 110,you will see part # 69-17834 for 68-78 corvette Ignition lock-with coded key set. 15.00$ free shipping I think.They have everthing for corvette's.