My TSC orders from Hoover's, some use other hatcheries also. Probably easy to find out for anyone who's not sure (and doesn't wanna call to ask) by clicking order live birds from the TSC site with your "home store" selected for.
2 out of 4 of the birds I got last year from TSC are throwing meat...
I'm not personally familiar with or heard anything specific to Seabright.
Malformation (in chicks) can be caused by a variety of conditions (like inadequate turning) as mentioned starting around page 53 of the following link with skeletal conditions mentioned later under certain nutrient...