Depending on the severity of damage to the rim, I thought the normal process was to take the wheel from the car, take the tyre off, sand/shot blast them to remove corrosion, a chemical dip to remove paint & dirt, a rinse to remove the dip and last of the dirt, filling of gauges, sanding, priming, powder painting & then being baked in an oven, lacquering, putting the tyre on & rebalancing.
This is assuming that the wheels aren't cracked or have their structure damaged someway. Otherwise there's more to do...maybe even have to write the wheel off.
The powder painting & baking is really the key to the finish. The cooking process breaks it down to give it an even finish that would be much harder to achieve with an aerosol style paint.
There are places that do aerosol spray kits for about £20, but I can't vouch for the colours.
It sounds like you've tried a couple already & not been happy with the results. For the money, I'd consider letting a local refurb company step in and do the job.