I'm afraid the only gun plugin you'll find that don't use spout will just be rapidfire arrows. Plugins with new models and textures and such can only be done with spout. So just get a spout gun mod. They probably aren't quite as widespread as bukkit TNT notifiers but there's bound to be a few.
Most of them are not possible without a client-side mode, hence the need for Spoutcraft as well. You could find regular hacked up mods that do the same, but in the end would be more work for the server owner and players.
Not plugins, but the Balkan's Weapon Mod and Modern Weapons are available for Bukkit. They don't use (not are compatible with) Spout but they do require all players install the client mod before they connect to your server. I use Balkan's Weapon Mod and it works great, highly recommended. However if you're looking for something not requiring any client mod, you won't find much, if anything. Server-only plugins are very limited in what they can do to change the behavior of the game; they can't add new items or entities. For the guns to be at all worthwhile, you really do need some kind of client modification.
I saw a plugin that used a glitched lever to simulate the shape of a lever that shoots arrows, but anything more than that and you are out of luck buddy
