You're going to be out of luck. All brake discs are made from cast iron and that corrodes, obviously.
The more expensive discs might come with painted or coated centres (I've even seen a few which are completely coated... the coating just gets worn off where the discs rub) but generally these are rare (peoples wants cheap, usually).
If you want resistant discs you could do worse than buying a set and spraying them yourself.
If it was me, I'd roughly mask off the main part of the discs (otherwise you'll get that paint coming off on the pads for nothing) and then spray;
a) The body of the disc, including about 5mm up onto the plate part
b) The top edge of the disc plate including about 3mm down the plate part
Use Hammerite (Smooth) in whatever colour does it for you. Silver or satin black might be better than yellow, red or white though.
Any overspray onto the disc plate where the pads touch will get worn off by the pads, so you'll get a nice clean edge.. so don't spend too long trying to get a precise masking off.
You also don't need to spray the inside of the disc (round the back) since it's out of sight.
Any discs plus good quality pads is better than expensive discs and cheap pads. Buy the cheapest discs you can find really... then use something like Brembo pads. Cheap discs tend to wear out more but it's the wearing out that gives the brakes "friction". Brembo pads will fit the calipers more precisely than cheap pads do and so won't jam.
Ralf S.
