Halfords do that (put paint in spray tins) but you need a code, trouble with spray tins is getting enough of them in the first attempt else it's difficult to get a match again.
Buy a compressor (Aldi do one that is fine for small jobs like a bike, maybe get a better gun (£20 - £25 ), Go to your nearest car paint shop, they will have a code and can get you what they call spirit paint ( acrylic or cellulose based as they use water based stuff these days) and thinners, all this will cost you £200 - £250 but you'll probable spend about as much on aerosols trying to get a match and you will still have a compressor and gun for other jobs or to sell on