I think that only situation where it would sound OK to use the preposition 'in' to connect 'opinion' and the subject in question would be a fairly general topic with a plural noun. You might possibly say "I have no opinion in these matters", where 'in' suggests 'amongst'. Otherwise, these are your main options: on about with regard to in regard to regarding (Note that 'in regards to' and 'with regards to' are not considered correct. They are very common native-speaker errors).

'Opinion in' is probably less useful than of/about, but it does sometimes get used. Such as: What is your opinion in this case? His opinion in regards to the matter was...