five or so years ago EBC had a larger front disc conversion available.
i bought one, it came wiv a bigger disc(rotor) and a carrier made out of aluminium(aloominum )

sadly, being sat on the bike for four years or so the carrier has rotted a bit, it wuz dead poor quality aloominum exposed to english salty roads

sorry i'm too wankered to work out how to post me piccies of it :-0

¿if you go here http://ebcbrakes.com/catalogue-enquiries/
and click on this link
European and other country motorcycle brake applications click here
it takes you to a spread sheet
search for CRM250 & i think the entry for
CRM 250 X Supermoto
is probly(maybe) the one i got?

The usual brake upgrade is to 320mm and the CRM250X is, I believe, an Italia Honda SM version of the CRF250. I would check with EBC what bikes they do 280mm discs for and what carrier might fit.