Why why do your two examples have to contain sherry combined with a second
wine? That makes it a bit like mezzo mix.
If asked for a sherry cocktail I would improvise but an important question is
what kind of sherry people like. Your Sherry Flip is a very nice suggestion
and has the sherry as main ingredient.
I am not suprised that Bippo doesn't have sherry in stock. It's more an
European drink.