strip everything off it, buy some sand paper and some gloss rollers, get the colour of coach enamel you desire and have at it yourself on a warm day. Far cheaper and more satisfying than paying someone else to do it, and unless you are looking for a very un-defender like metallic colour will give a perfectly good finish for a defender. if you have the willing you could even try to spray it yourself, plenty here have had good results it is just not something I have ever tried.
If you are planning on a metallic colour then may I recommend choosing a better colour. Land rover peaked when their colour choices were only below. Pick one of these and have at it yourself
Look at paintman and speak to them. You almost certainly will be able to.
I get my paint from a local supplier who mix to order. So I could go to them and request Epsom or aintree as a coach enamel and they would make it while you wait.