All Legion branches will have the flags. Some have specific uniforms, bought by the Branches, for their Colour Parties. If not, the normal Legion "Blues and Greys" (blue blazer and grey slacks) and Legion beret will suffice. If your doing it in your own uniforms, make sure everyone in the party is the same, and well turned out. As far as rifles, if the Branch does not have any, another Branch in the area may be able to help. Armed Escorts are not really required, some use them, some don't. It's not a big deal. Get the commands right and do some practices before hand. Recce the spot of the ceremony and ensure you have the room to manoeuvre and how your going to do it. Is it a large hall full of dinner tables, or a weirdly laid out funeral home? It's always best to check and run through a couple of practices first. Also speak to the President or the Committee for any Branch customs they follow. The Branch has likely had their own do this before, and past Colour party members will be able to help you out as to what they're looking for.
BTW, good on you and your compadres. It's nice to see young people getting involved with the Legion. They need the help. Let us know how you made out.