There are some really large racing type flares available now, but for something more sedate most people are using flares cut from old Dodge Omni's or Plymouth Horizions and welded to the body. I've heard that early VW Rabbit flares work well also, very similar in shape to the Dodge units. These are getting harder to find that aren't rusted out, but they are still out there if you look. There are som photos of a set mocked up on the Project Roadmaster GT on this page http://forum.britishv8.org/read.php?2,166,page=13
There was a good discussion on this topic with a lot of photos also on the MG Experience board last month. http://www.mgexperience.net/phorum/read.php?40,755214
'73 Midget (V6)
'59 MGA (I6) under construction
"There is a fine line between a hobby and mental illness"