Oh yes, you’re out of luck, N64, Gamecube and Wii are some of the most expensive consoles when it comes to RGB/YPbPr.
For the Gamecube and Wii (I assume they would be compatible with the Wii), your best option seems to wait for this : https://www.retrorgb.com/insurrection-industries-announces-sub-100-gamecube-component-cable.html
The price is steep, but if you look online how much cost official YPbPr cables for the gamecube, you will see those $100 as a bargain.
From what I’ve heard, the N64 RGB mod isn’t the most complicated or at least the most expensive mod out there, but you’d still have to spend, at least, an additional £20 for a cable (https://www.retrogamingcables.co.uk/nintendo/n64).
You did things in a wrong order I’m afraid, usually people get the cables and then the OSSC (or Frameister or whatever).
You are not informed enough, no offense, you can’t blame someone for not knowing that he doesn’t know something. So I’m going to try to put you on the right tracks :
This is a playlist of 37 videos, the first ones will teach you the basics (RGB, sync etc) and the next videos will talk about “each” console and get into the specifics. Don’t worry, you’ll love watching these ! I’ve watched some of them 5 times !
In addition, you should read this site : https://www.retrorgb.com/rgbguide.html
There is also a section where you can check each console :
Wii : https://www.retrorgb.com/wii.html
N64 : https://www.retrorgb.com/n64.html
Gamecube : https://www.retrorgb.com/gamecube.html
The SCART cables that you’re using right now, they look like SCART RGB, but they are wired differently. Basically :
Composite SCART : Red, green, blue, sync H, sync V and luma go through the same pin (so, through a single cable, it’s exactly like using a single Yellow RCA)
SCART RGB : Red, green, blue are all on separate pins (so, on separate cables).
That’s the easy version, it gets more complicated but it’s not out of reach. The sync is the most complicated thing when you start, watch the first 2 or 3 MyLifeInGaming videos up to when they explain the sync. Then you can use this homemade chart below to help you with your future purchases :
Left : name of the sync signal
right : details of the sync signal
for instance, “Y+C+s” means that all of these things are in the SAME cable,
“R/G/B/s” means that all these things are in SEPARATE cables
so “+” means “combined into the same cable/pin”
and “/” means “separated from the rest”
Ideally, each thing should have its own cable, so have as many “/” as possible.
Y = Luma (black and white, luminosity)
C = chroma (chroma means R,G and B are combined)
R,G,B = Red, green and Blue
s = sync (“s” alone means that sH and sV are combined)
sH = horizontal sync
sV = vertical sync
RF______________________Y+C+s (+audL+audR)_<- you don’t want that
Composite_______________Y+C+s______________<- that’s what you have
All those sync signals are basically ordered from the worst to the best. Ideally, you want anything below Y/C (S-Video).