PreludeRM said:

But really there is no equivalent as the 501st do think they are better then everybody and any costume group.

That bears repeating. If I'm not mistaken, there were a few members from the Rebel Legion that were in that parade too, but the lions share of the costumers were 501st members.

I also find it interesting that they were at one time all one group. "The worst thing we ever did was split the rebels out into their own group" - A former 501st LCO.

Whatever you do, do not join the Rebel Legion hoping to get any recognition at events. Time and time again, both groups will show up but the only one you'll hear about is the 501st.