The following sets (as far as I know) are currently on loan to SNCF:
3203/4
3225/6
3227/8
3301-3314 (ie all regional sets)
They mainly see use on the LGV Nord, being still based at Paris Le Landy, on the Lille-Paris corridor section services. Every now and then, one or two will head south to (iirc) Lyon.
It all depends on where SNCF have the shortage of TGV sets! You can still tell that they are Eurostar sets though...some still have the yellow front ends, whilst they maintain the "rounded-nose" of the Eurostar, rather than the more pointy nose of the TGV.
Cheers
Dave