To answer your query, you will definitely be able to locate the DMG files and other development tools on https://developer.apple.com/download/more/ This will require you to sign in using your Apple ID. In order to have a valid session, after logging on, you will then be able to download the links given below for subsequent versions starting from the earliest version right upto the 13 XCode version.
12.5.1 This version will need a Mac with Apple silicon running macOS Big Sur 11 or an Intel-based Mac running macOS Big Sur 11.
12.4 This version will require a Mac with Apple silicon running macOS Big Sur 11 or an Intel-based Mac running macOS Catalina 10.15.4 or later.
12.3 This version requires a Mac with Apple silicon running macOS Big Sur 11 or later, or an Intel-based Mac running macOS Catalina 10.15.4.
12.0.1 This will require a macOS 10.15.4
Xcode 10 which is not supported for iTunes Connect
10.3 This version requires macOS 10.14.3
10.2.1 This version requires macOS 10.14.3
10.1 This is the final version which supports the macOS 10.13.6 High Sierra
Even Older Versions which are unsupported for iTunes Connect