Re:
Its very likely they have faded considerably over the last 30 years. Marin dayglow just did. So even if you can find the colour it now wont be the same.
Movac and other automotive paint suppliers can normally colour match to an item and give you a dedicated spray can. But, colours like this are hard to reproduce.
You may just have to go with the nearest touch up you can from halfords etc. Take the bike in with you and see what they have. If its only small bits you may not notice too much.
Sadly, it you really cant live with it, it may be time to bite the bullet and respray the forks, bars and stem. Quite do-able at home with a bit of prep and patience. Halfords do have a dayglow range of colours in cans and laquers. Never used them, but others here have, to good effect.