I was reading Forgotten Realms and I encountered Gond, an intermediate god of crafting and invention. His worshippers had invented something called an arquebus(?), which was basically a gun that had a high chance of self-detonating.
I'm wondering if this is in the game anywhere, or if anyone has made one.
There probably isn't one. Guns in D&D are hard, and 4e is probably the worst edition for it. I'm saying this as a fan of 4e. 4e values balance. Guns are hard to balance when you take "real life" into account.
As soon as guns enter the equation, people talk less about balance and simplicity and more about realism. Any realistic gun tends to have a long reloading time. There's often special rules about wet powder (I've never seen official rules for wet bowstrings), smoke creating concealment, etc. People just know too much about guns.
D&D doesn't do realism well. Just look at how unrealistic a crossbow is. It has a range of only 15/30, so that's a range of 150 feet if you haven't taken Far Shot. Needless to say, that takes away a bunch of the crossbow's advantage. It has a load time of minor, which is far shorter than it would have been in real life. In real life, a crossbow is pretty useless as a single person weapon, but devastating in groups. You shower your opponents with bolts from long range, and then you laboriously reload and do it again. You want to do this from long range so you have time to reload several times before you have to run into the forest or behinds those stakes you pounded into the ground for cover. This ... doesn't suit a system design for small groups armed with different weapons (if you count magic as a weapon) who often fight in dungeons or cities.
Early hand-carried guns were mass battlefield weapons. They were too inaccurate and slow for adventuring use. If you make them realistic, you don't want to be using them in D&D.
Also, are there any other items that are Gond related? (clockwork,etc.)
I don't know about items, but the Craft domain had some cool domain-only spells. I really liked Fantastic Machine, and even converted it (as a monster, not a spell) for 4e.
Also, is there such thing as a cleric of Gond? what would that class involve?
Yes...
IMO, NPC priests do not need to be clerics. One thing I liked about 4e are NPCs don't have to use the same classes as PCs. You just give NPCs abilities that "fit". An NPC priest of Gond might not know anything about healing, and might have some non-magical ability to create minion traps (land mines). They might not be team players and won't find abilities like Priestly Laser useful. Radiant damage? Why? They don't need Turn Undead, Rebuke Undead, the invoker's Stun Undead, or whatever.
IMO, a PC cleric of Gond needs to suit an adventuring party. That means spellcasting, healing, and non-lame armor proficiencies. A PC cleric of Gond is special and suited for adventuring, unlike the majority of priests of Gond. If the player wants to create a character who doesn't suit a party, thank them for designing an NPC for you, and have them try again. It's possible some players shouldn't play priests of Gond due to self-nerfing desires.
Quite a few Gondsmen won't be divine spellcasters. They might be (in 3e terms) experts instead. That's fine, but they're not adventurers, they're minion NPCs who can make friends (or support enemies) when it comes to PCs.
