Amazing how well it all blends together! There is a bit of deleted ROTJ footage in Battle For Endor if you know where to look.
Sharp eyed viewers would note they aren’t using Imperial weapons. How to explain that away? Create a line of dialog about the Rebels giving them some? It’s believable that some of the Rebels weaponry might be a bit worse for wear at this point.
Another possibility is making Noa’s ship this mysterious, almost ancient derelict smuggler’s wreck in the forest, which biker scouts regarded as no threat to the Imperial base. The Ewoks go there in desperation to get their blasters. Now that they’ve seen Rebels and Imperials using blasters they finally realize what all the weapons on the ship can be good for!
The Ewok glider could drop explosives perhaps? Even if they are ineffective against Scout Walker armor, it would be an improvement.