i got mine from ford for 177.
i coulda got them for free out of my 7.5, but i didn't want to take the chance since I *threw* my 7.5 out of my truck bed.
As far as junkyards, here they make you buy the whole thing (i.e. rear axle) and they don't let you take anything apart in the yard. So I would have to buy a new axle, 400+, for a 177 part that is BRAND NEW
If your like me and just want a new part, go to ford, I could even possibly get the part number for you and you could get i off firstfordparts.com
I'd have to do some searching for the recipet though. And the left and right sides are different lengths, so be specific
08 Cummins Mega Cab, 7" on 37
02 Explorer Sport
08 Brute 750 on 29.5