Public Function CountStrIn(ByVal cSearch As String, ByVal cFind As String) As Long
' cSearch - что ищем, cFind - где ищем
    Dim i As Long
    CountStrIn =  0 
    i = InStr( 1 , cFind, cSearch, vbTextCompare)
    While i >  0 
        CountStrIn = CountStrIn +  1 
        i = InStr(i +  1 , cFind, cSearch, vbTextCompare)
    Wend
End Function

Dim v As Variant, nCount as Long
v = Split("Мама мыла раму, рама мыла маму. На дворе трава, на траве дрова", "а")
nCount = UBound(v) - LBound(v)

Dim v As Variant, nCount as Long
v = Split("Мама мыла раму, рама мыла маму. На дворе трава, на траве дрова", "а",- 1 ,vbTextCompare)
nCount = UBound(v) - LBound(v)