I've read this question about why it is not possible, but haven't found a solution to the problem.
I would like to retrieve an item from a .NET
/// Determines if this set contains an item equal to <paramref name="item"/>,
/// according to the comparison mechanism that was used when the set was created.
/// The set is not changed. If the set does contain an item equal to
/// <paramref name="item"/>, then the item from the set is returned.
bool TryGetItem<T>(T item, out T foundItem);
This is actually a huge omission in the set of collections. You would need either a Dictionary of keys only or a HashSet that allows for the retrieval of object references. So many people have asked for it, why it doesn't get fixed is beyond me.
Without third-party libraries the best workaround is to use
Dictionary<T, T> with keys identical to values, since Dictionary stores its entries as a hash table. Performance-wise it is the same as the HashSet, but it wastes memory of course (size of a pointer per entry).
Dictionary<T, T> myHashedCollection; ... if(myHashedCollection.ContainsKey[item]) item = myHashedCollection[item]; //replace duplicate else myHashedCollection.Add(item, item); //add previously unknown item ... //work with unique item