You can find the DMGs or XIPs for Xcode and other development tools on https://developer.apple.com/download/more/ (requires Apple ID to login).
You must login to have a valid session before downloading anything below.
*(Newest on top. For each minor version (6.3, 5.1, etc.) only the latest revision is kept in the list.)
Xcode 13
13.0
Xcode 12
12.5.1 (requires a Mac with Apple silicon running macOS Big Sur 11 or later, or an Intel-based Mac running macOS Big Sur 11 or later) (Latest as of 22-Jun-2021)
12.4 (requires a Mac with Apple silicon running macOS Big Sur 11 or later, or an Intel-based Mac running macOS Catalina 10.15.4 or later)
12.3 (requires a Mac with Apple silicon running macOS Big Sur 11 or later, or an Intel-based Mac running macOS Catalina 10.15.4 or later)
12.2
12.1
12.0.1 (Requires macOS 10.15.4 or later) (Latest as of 24-Sept-2020)
Xcode 11
11.7 (Latest as of Sept 02 2020)
11.6
11.5
11.4.1 (Requires macOS 10.15.2 or later)
11.3.1
11.2.1
11.1
11 (Requires macOS 10.14.4 or later)
Xcode 10 (unsupported for iTunes Connect)
10.3 (Requires macOS 10.14.3 or later)
10.2.1 (Requires macOS 10.14.3 or later)
10.1 (Last version supporting macOS 10.13.6 High Sierra)
10 (Subsequent versions were unsupported for iTunes Connect from March 2019)
Xcode 9
9.4.1
9.3.1
9.2 (Last version supporting macOS 10.12.6 Sierra)
9.1
9.0.1
Xcode 8
8.3.3
8.2.1 (Last version supporting OS X 10.11.5 El Capitan)
8.1
8.0
Xcode 7
7.3.1
7.2.1 (Last version supporting OS X 10.10 Yosemite)
7.1.1
7.0.1
Xcode 6
6.4
6.3.2
6.2 (Last version supporting OS X 10.9.5 Mavericks)
6.1.1
6.0.1
Even Older Versions (unsupported for iTunes Connect)
5.1.1 (Latest version supporting OS X 10.8 Mountain Lion)
5.0.2
4.6.3
4.5.2
4.4.1
4.3.2
4.2
4.1
4.0.2
3.2.6
3.1.4
3.0
2.5
2.4.1
2.3
2.2.1
1.5
1.0