Community-maintained archives often host these versions. A known directory for these files is often linked in the Mobile01 discussion thread or the Logout.hu forum .
This is the primary source for TCL firmware. Search the TCL Android TV or Thomson TV threads. You will likely find the "part05.rar" as part of a larger split archive.
If you are performing a "deep" update, you usually need the .pkg file (for USB recovery) rather than the smaller .zip OTA update. Make sure the file you extract is named correctly (e.g., Update.pkg ).
TCL 50P6US 50吋4K 簡易使用心得分享(第33頁) - Mobile01