Classification of irreducible $(\mathfrak{g},K)$-modules for $SL_2(\mathbb{R})$ and $SL_2(\mathbb{\mathbb{C}})$ can be found in many standard textbooks, like Wallach's "real reductive groups". I am wondering whether there are any references which treat such classifications in great details for other small rank reductive groups, like $SL_3(\mathbb{R})$ ($SL_3(\mathbb{C})$), $Sp_4(\mathbb{R})$ ($Sp_4(\mathbb{C})$), and $G_2(\mathbb{R})$ ($G_2(\mathbb{C})$). Since local Langlands correspondence for complex and real reductive groups are known, representations of such groups should be understood very well and the classification should be known. I am just looking for a reference for such small rank groups.
I understand that Duflo has a paper on irreducible unitary representation of groups of rank 2, and Vogan has a paper on irreducible unitary dual of $G_2(\mathbb{R})$. But I am not sure they treat the classification of all $(\mathfrak{g},K)$-modules for such groups. The first one is in French and the second one is very long. I did not read them carefully but it seems that most parts of their papers are proving certain representations are unitary. I am wondering if there are some notes which only treat the classification problems.
Any comments are references are welcome. Thanks in advance.