"I'll just get someone else to talk to you who knows more about this than I do.."
"I'll just get someone else to talk to you who knows more about the matter/this..."
"I'll just get someone else who can help you with that."
Notice: with the first sentence you may be somehow "admitting defeat", which in some circumstances (mostly at workplace, to mention one).
As you want something more polite, you could adjust those to something like:
"Let me get someone else who can be of help with that, he/she knows a lot about this matter", OR by way of explanation - "he has more years of experience under his belt".for example.
I don´t recommend the "let me put you through to someone else", because it suggests you are on some sort of switchboard, or some PABX system, so you are connecting the caller to the receiver of the call.
It´s my educated opinion here though.