Here's what I found specific to your case dated May 10, 2011: the C1 can now be found.
As with everything hardware with newer Apple stuff, lack of info means it's done the hard way or not at all. I've done it the hard way so you don't have to. The newer part number for the mid 2010 iMac screen doesn't even exist on the internet yet. (until now)
27" Late 2009 Core Duo uses LG screen LM270WQ1 (SD) (A2)
27" Mid 2010 i3, i5, i7 all use LM270WQ1 (SD) (C1)
The difference is NEARLY none, except one single thing. They changed 1 plug for no apparent reason but to screw with you. The part numbers on the controller boards are the same, everything else is the same. They simply changed the connector. It's not stronger, bigger, nor better suited, it's just "different".
You may notice the (A2) screen is beginning to pop up a few good places now, but the (C1) screen doesn't even exist on google. ......at all.
To remedy this if you have to replace the screen, buy the (A2) screen and swap the controller board in question with your old one.
The board with the WHITE PLUG is the Late 2009 Core DUO.
The board with the BLACK plug is the Mid 2010 i3,i 5, i7.
This plug can be seen in the pics below in the first picture the plug is closest to you in pic #1, small, and it is a 4 pin plug to the right of the copper square.
This board is dead center at the top rear of your LG 27" screen. It's only about a 5 minute job.