People always said "the GC versions of RE2-RE3 are straight ports of the PSX version", because people are dumb and only look at things at surface level and claim things they know nothing about and other people parrot that.
They're actually ports of the PC versions, the file structure is identical (unlike the PSX version) though in the case of RE3 uses it also PSX versions data fo fix certain things that were wrong in the PC version like some backgrounds that were wrong (that's another rabbit hole you don't want to get into because once you know about that, you can't unsee it and you won't enjoy the PC version anymore even though you currently probably believe it's the best version of the game; but I'll be happy to oblige if you really want to know).

Anyway what I'm getting at is that the 2 costumes that were exclusive to the PC version of RE3 (I'm not counting the DC version because the DC literally is the PC version running on Windows CE) are actually present in the data of the GC version even though they were made inacessible to the player to imitate the PSX version.
And within those files there is more, there is a third costume which doesn't exist in the actual PC version, costume which was therefore presumably made for the PC version but went unused and was left in the files of the GC version by accident. You can copy paste and rename that costume to use it as is in the PC version, webm related.

>>11842241
PC/DC versions have 2 extra costumes.
On top of that this red one is an unused costume which was made for the PC version but found unused in the files of the GC version (because unlike the common belief that the GC versions of 2 and 3 are "ports of the PSX version", they're actually mostly based on the PC versions), I just took the file and copy pasted it in the PC version