In the same boat. A mate of mine is looking at on online place that makes touch up paint. Will make it in small bottles up to rattle cans. I'm considering looking into that as the resto suppliers want an arm, a leg and a left dangly for a can of spray. Just thought it would be useful in the engine compartment like you and perhaps in the boot where I have some of the paint gone.
I'll have to see who he is using and what their prices are. Guess I could always try buying a cheap touch up gun and spraying it, but the price of the automotive paint at suppliers here is outrageous anymore.
Cheers