I am a sculptor and putting clear coat on bare steel will not work.
It will only last one year at most.
The best thing to do is to have a painter mix paint that looks that way and then clear coat that.
Make sure to sponge on or dip the entire frame into a phosphate bath or just use phosphoric acid with a sponge. Leave it over night till it all turns grey. Then the rusting process is stopped.
The put on primer, paint, and clear coat or get it powder coated.
Many powder coat places sand blast, give it a phosphate bath and then powder coat.
Then you have a real good frame.
On a Roadstar Adventure.