Nick:
Sq D makes a lug that bolts onto the ground buss bar, but you have to ask for it and its extra.
When I first started i liked Sq-D and ordered a 100 amp service panel and at the time it went for about 60 dollars, and accidently I asked the kid behind the counter is the cover included ? He said, No, thats extra, how can a company survive like that ? I dont know he said, but thats policy.
and this is just another 'trick' of the SqD company. Now you can buy a QO panel and the cover is included, but from what I have seen this is typical.