Where can I find the old version of the Mint app for iOS 4? I'm on a jailbroken iPhone 4 running iOS 4.3.5. There is still not an untethered jailbreak for iOS 5, so I am not able to upgrade yet.

Mint has gotten a bit ahead of themselves and released a new version of their iOS app that requires iOS 5. The old version supported on iOS 4, but it is no longer available. There has been some talk on their support forum about the issue, but there doesn't seem to be a solution.

Where can I find the old version of the Mint app that supports iOS 4?
Unfortunately, This is not possible due to current App Store limitations unless someone else with a jail broken iPhone that you trust has a copy of it that you can grab. One problem with dealing with the Apple App Store is that older versions are forever lost due to Apple's App Store polices. We should be giving concerned feedback to Apple to address this issue too, not just the app developers. So it looks like your best option if you need to have the Mint app, is to read up on the latest jailbreak, and insure your jailbreak path, then update your iPhone to the latest iOS, and then re-jailbreak it. The good news is that there is a untethered jailbreak for both iOS 5 and iOS 5.0.1 for the iPhone 4 as referenced in my comment above.