Yeah, there are a million different quick-release clasps that you can buy at Lowes, Home Depot, or even Walmart, and since it's on the outside of the cage, if you put the clasp at the bottom of the door he won't be able to get to it, so you can use something like a heavy Caribiner or similar without worrying about him getting his beak caught in it or anything...
Walmart sells an entire line of different Carabiners, everything from cheap ones for $1 a piece to climbing-grade that cost $20-$30 a piece in their camping section...I do a lot of mountain biking and fishing, and I got tired of paying for equipment at Dick's or any of the other "outdoor" stores, so I started buying my stuff at Walmart (except sleeping bags or tents)...The older you get, the less you care about "brand names", lol...Anyway, there are a bunch of different clasps you could find....
My very first Budgie that I was given when I was 6 years-old (circa 1986) had a cage like this, it was an awesome cage that was huge and sat on a tabletop, and the bars were heavy-gauge metal, but it was round, the entire cage was round...It has a sliding door, and my Budgie figured it out...So my mom used a regular old twisty-tie, lol, and it was a pain in the butt to untwist and then twist again a million times a day, but it worked...i wish she had known what a Carabiner was, lol...