i lost some for my apps how can i get them buck

Sorry, but the only apps you can install are apps from the app store & if what you want won't work on your phone, other than purchasing a new iPhone, there is nothing you can do.

iOS 4.2.1 is the end of the line for the iPhone 3G, & that model has been discontinued by Apple. It is what it is.

Developers determine what iOS versions their apps support, not Apple.