where were the collosus computer parts made?

The Colossus machine was valve (vacuum tube) based, and the bulk of the parts would have been normal electronic components no different to those used to make radio receivers and record players etc. in that era.

They would have been manufactured mostly by the English or British makers of such parts, eg. Mullard, Cossor, Brimar, Mazda etc. 

Other than the memory systems for relatively large scale data storage (such as magnetic drums, delay lines or core memory planes) electronic computers used standard mass produced components [plus custom circuit boards and casings etc.] through to the end of the 1960s at least.

It was only when customised integrated circuits became practical that computers got beyond the point that anyone could in theory build a copy from the circuit diagrams in the service manuals!

The computer in the movie "Colossus: The Forbin Project" was mostly just stagecraft.  That is the technique of making cheaply something that looks expensive.  It is not functional as well.  So most parts were from scrap, with a few operating things thrown in (tape drives, monitors, keyboards, electric lights).

https://en.wikipedia.org/wiki/Colossus:_The_Forbin...

I worked for Disney doing "Imagineering" at WED Inc.  I made a lot of display mockups for the entertainment park rides.  Scrap stuff was the best choices for those.  However, the final versions had to be highly developed by the engineering staff.  This was because of dangers possible to guests at the very complicated and sometimes not accessible inner spaces.  That is where all things had to work perfectly all the time for months if not years.  So safety and durability were most important.  Fire was alway lighting tricks, smoke or mist was CO2 or liquid nitrogen discharges or water vapor.  No contact to anything fragile or electric by anyone was possible. 

Made in China   

Whatever parts that weren't made in house or sourced in the UK likely came from the US.

RCA, General Electric, AT&T and IBM likely supplied valves, relays and tape readers.

The Colossus computer was made by General Post Office (GPO) engineers, parts would be bought in  from a number of manufacturers. 

I'm going to guess either Rhodes or New York as those are the only two places known for having a "colossus" (note the spelling).