Hi Rocky
There's a company in the UK called
RS Bike Paint. Click for link.
Use the colour code that is on the label stuck to the frame under the seat.
Read their blurb carefully - if it is a metallic or a candy colour, you will likely need 3 different paints. A base (silver flecks if it is metallic), a translucent colour coat and a lacquer. The paint isn't necessarily waterproof until the lacquer has been applied.
Getting an exact patch is almost impossible. The reason being that the colour changes as soon as you apply the crystal clear lacquer - it gets lighter and brighter - quite significantly so. But a very good approximation is definitely possible. But its expensive - 3 cans at around £25 per can. iirc.
I got an old plastic glasses case. Applied a few layers of base. I did it by misting - a quick swipe left to right, starting away from the case and finishing beyond the case. The first misting doesn't cover it. Its only about the 4th or 5th that you can say the whole surface is beginning to look covered. Let it dry between each coat (which doesn't take long).
Then I masked off all but a narrow strip of the case and used the same technique with the colour candy coat. Let dry.
Then I removed the mask and applied a new one - leaving a strip twice as wide as before (including the bit that had received one mist of colour. Applied another misting.
So now I had two strips that had been misted. One strip had received 2 colour mists, one had received just one.
Let dry.
I then repeated the same pattern, applying a new mask to expose another strip of unpainted plastic. and kept repeating until I had 9 strips. The first strip had received 9 coats, the second had received 8 coats, the third had received 7 coats and so on.
This was left to dry, and then I carried out a similar process - but this time masking off 3 strips across at right angles to the first set. This was to apply the lacquer. 1 strip received one coat, one received 2 coats, 1 received 3 coats.
At the end of all of this, I had 27 different shades to hold up against the original bike paint.
In this way I knew how many mistings of colour and how many of lacquer were required to get the same results.
Its a mistake to be tempted to hurry it by taking it slowly with the spray in order to cover more. The paint will 'pool' and run and will be uneven. The first few coats will result in something which doesn't look painted. But gradually it builds up.
As I say - expensive. Its tedious and doesn't guarantee an exact match. When I did mine, it was pretty much spot on - in every photo that I took. But then I'd see it in a different light and I could tell that it wasn't quite right.
You wonder why there were so many different shades of Candy Red for the 1300s ? I think I know.