Toplac can give a brilliant result! but strongly suggest that you use jenny brushes for laying off, after applying with a roller... Varnish/gloss type...that way no brush marks..no connection just an impressed user.
I assume from your post that your question is more about where you can get the colour you are after?
If the marine paint suppliers can't help then you could try thr car paint suppliers. You would definitely be able to get a suitable colour from them. Make sure though that you speak to someone who knows what he is talking about. Car paints are usually sprayed, so you would need the right additives/thinners for brushing/rolling to work properly. The same applies to any undercoats and primers you may use.
It won't be cheap though.....but using marine paint wouldn't be either!
You could go to a good automotive paint supplier, every town or city has a spot that does everything required, and get Coach Paint. It is formulated for brushing and can be mixed in any colour. Lots pof places don't do coach paint nowadays, but it is still available.
Coach painters , before the days of space heating, used to put the paint pot in a bowl of warm water to keep the paint at a flowing temperature.
You don't say where you are but Smiths in Kent may be someone to ask.