I went to my local paint shop to buy some Diamond White, the shop assistant asked me which shade, to which i thought he was pulling my p*sser. He told me there are 16 shades of Diamond White . So, i'm pretty sure you'll be able to get a colour match for your car, you should have a paint code on 1 of the tags on the slam panel under the bonnet, quote that when you ask for the paint. Buy more paint than you need, as there can be slight differences in shades between batches/mixes.
To powder coat, the item is electrostatically charged, then sprayed with the powder. The part is then baked in an oven to harden the coating. So, powder coating, though not impossible, probably isn't an option. Powder coating is affordable. There's another topic on this forum 'Saff underderside restoration' or similar, ask that guy for prices, as he had all his rear suspension components done not so long ago.
Probably aint gonna make any friends for saying this ( no offence intended ). Classic car restorers generally steer clear of Hammerite, as it drys (eventually, about six weeks!) very hard. Hence it chips easily. I don't see why you could't brush 2 pack on? Havn't a clue what it would turn out like though? I'd spray, or get it sprayed myself.