If you need older apps for your older iPod Touch, you can try to download the latest app from the iOS App Store and if the developer has left an older, compatible version on Apple's app servers, then you will receive a small window pop-up prompt that states that there is an older version of the app that is compatible with your device. Would you like to download this version now.
Tap the OK button just below the prompt.
FYI,
Not every app you attempt to download will have an older compatible version. For older apps that may still have an older iOS version available, the lowest compatible iOS version of an app is iOS 4.2.1.
The search for older, but compatible apps will be trial and error, but they are out there.
I have older iDevices that have older, working compatible apps and these devices have over 100 apps on them.
Games maybe a big issue of finding an older, compatible version that'll run on your older iPod Touch.
This website may help you locate older apps you can use with your older iPod Touch
http://findoldapps.com/
Good Luck!