In the UK, there's etsy, Shpock, and Gumtree, but none of them will yield big money for you. As mentioned before, there's probably more value sentimentally than financially, unless you happen to find someone who met their first love at that convention, or has significant other meaning attached to the inlay. You might get £25-35 for it, or you can keep it as a memento, and carry "Dad's knife" everyday.