Well the way I perceive the construct 'your + plural', where the plural is a plural of a unique noun is
this is a metaphor; in your first example it refers to blue-chip stock, in second example it refers to top baseball players
it is a metaphor because it refers to 'your IBM' and 'your Cobb' - IBM is not your neither is Cobb; it refers to 'companies/players that share attributes with IBM/Cobb'
repetition clarifies what the common attribute is
The following does not really touch on the details why plural is useful here, but since an attempt had been made to classify the rhetoric figure used, I will comment on that.
I feel that 'part for the whole' (pars pro toto) is related, but that it is not a defining trait.
Let me present two figures I believe are more relevant. First is called interpretatio and it deals with the repetition and another is antonomasia and describes the type of metaphor used in each repetition:
1) synonymia (specifically interpretatio)
In general, the use of several synonyms together to amplify or explain a given subject or term. A kind of repetition that adds emotional force or intellectual clarity
You blocks, you stones, you worse than senseless things! ("Julius Caesar", Shakespeare)
Give me your tired, your poor,
Your huddled masses yearning to breathe free ("The New Colossus", Emma Lazarus)
2) antonomasia (also periphrasis)
Substituting a descriptive phrase for a proper name, or substituting a proper name for a quality associated with it.
He proved a Judas to the cause.
Here "a Judas" stands for "treacherous".
Similarly in the case of the "your Ruths, your Gehrigs, your Cobbs, your Killebrews" it stands for "legendary", in case of stock for "blue-chip".
However, originally antonomasia does not need repetition to clearly point to the attribute, where the quotes in the question became more clear through interpretatio.
Finally, I don't feel that synedoche (pars pro toto) is a good match to describe the figure used here.
A whole is represented by naming one of its parts (genus named for species), or vice versa (species named for genus).
Listen, you've got to come take a look at my new set of wheels.
Here and in other examples that I found the metaphor literally uses a part to refer to a whole and not an instance of a class to refer to a class (as we have in the examples from the question).