No chance to get older app versions for iPhone 3G

I own a iPhone 3G and a iPad 2. Today I had to restore my iPhone to factory content. I made an encypted backup hoping to get all my apps back on the iPhone. The restore from the backup didn't re-create my apps, just the standard apple ones. Syncing the apps with my iTunes library didn't work, because they are almost all newer versions which work on the iPad don't work on my iPhone in iOS 4.2.1. This is crazy, I paid for them and can't get them back. Any solution? I'm desperate!