Sorry to say Apple doesn't offer one and I have yet to find any 3rd party offerings.
Your options are:
- Get a spare MagSafe charger and use the AC cord with it to extend it that way using the charger instead (which is what I would do).
- If you have a dead charger (still has a good cord) you could try to create you own using a MacBook MagSafe DC-In board. You'll need to find someone with a 3D printer to make a case for the board.
Also remember adding length here on the DC side will drop the voltage so I'm not sure if that could effect the SMC charging logic.
If on the other hand you are talking about the Thunderbolt display connection:
So far I haven't seen one offered. That is if you want to use the ports on the Thunderbolt display.
If you only want to use the DisplayPort part of the connection there are a few DisplayPort extension cables like this one: C2G Mini DisplayPort Extension Cable, Male to Female (6', White) this is what we use but we're connecting to a DisplayPort display not a Thunderbolt display unit. So I'm not sure if this will work here.
The other option, is to open the display and carefully remove the current Thunderbolt cable from the socket on the logic board and then feed through a longer cable! Replacing the current combo cable.
Review this IFIXIT guide: Apple Thunderbolt Display Teardown jump down to Step 10 where you can see the connection is just a simple plug & socket connection.
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You are speaking about the MagSafe power cord side not the Thunderbolt display/data cable correct?
crwdns2934271:0crwdnd2934271:0 Dan crwdne2934271:0