I maybe missed some skins because they aren’t available in the Shop atm or just isn’t that unique from the basic look (just another colour tint), but here are a list about all the Heroes and how many Skins (not colour tints) they have in December of 2019:
A
Abathur: 4
Alarak: 3
Alexstrasza: 3
Ana: 2
Anduin: 1
Anub’arak: 4
Artanis: 4
Arthas: 5
Auriel: 4
Azmodan: 4
B
Blaze: 2
Brightwing: 5
C
Cassia: 3
Chen: 3
Cho’Gall: 3
Chromie: 5
D
Deathwing: 1
Deckard: 2
Dehaka: 3
Diablo: 6
D.Va: 3
E
ETC: 5
F
Falstad: 3
Fenix: 1
G
Garrosh: 3
Gazlowe: 4
Genji: 3
Greymane: 4
Gul’dan: 3
H
Hanzo: 2
I
Illidan: 5
Imperius: 1
J
Jaina: 6
Johanna: 5
Junkrat: 3
K
Kael’thas: 5
Kel’Thu-freaking-zad: 1
Kerrigan: 6
Kharazim: 6
L
Leoric: 5
Li Li: 5
Li-Ming: 7
Lt.Morales: 4
Lúcio: 3
Lunara: 5
M
Maiev: 2
Malfurion: 4
Mal’Ganis: 1
Malthael: 3
Medivh: 2
Mephisto: 1
Muradin: 5
Murky: 5
N
Nazeebo: 5
Nova: 6
O
Orphea: 2
P
Probius: 2
Q
Qhira: 1
R
Ragnaros: 2
Raynor: 5
Rehgar: 4
Rexxar: 3
S
Samuro: 3
Sgt.Hammer: 4
Sonya: 7
Stitches: 6
Stukov: 2
Sylvanas: 5
T
Tassadar: 3
The Butcher: 4
The Lost Vikings: 2
Thrall: 3
Tracer: 4
Tychus: 5
Tyrael: 4
Tyrande: 5
U
Uther: 5
V
Valeera: 5
Valla: 7
Varian: 4
W
Whitemane: 3
X
Xul: 4
Y
Yrel: 2
Z
Zagara: 4
Zarya: 4
Zeratul: 6
Zul’jin: 3