Have a look at the codes on the slam panel.
Bear in mind that aerosol paint is only 1k,as opposed to base coat and lacquer that is probably on your vehicle
Any auto paint suppliers should be able to accomodate.
Bear in mind though that they do have a minimum quantity ie 250ml paint and not all do an aerosol.
Try a main dealer re price before you try Halfords.
I bought as aerosol from them ,300ml if I remember for £9.99,and the colour was not quite right .However it didn't matter as it was for the rear boot floor.
I later bought a geniune paint touch up kit from an independant dealer ,and not only was it cheaper it was an A1 colour match.
The kit was basically an aerosol of paint and lacquer.