Aprilia 250s, die-cast or plastic kits, are rare as hens teeth for some strange reason. I know this cos I did a lot of searching for them myself. Really odd when you consider the number of World Championships theyve won.
As far as I know, there are no Campatella Aprilias available at all, however there are a few Aprilia 250s, in varying scales. If you really want a Campatella one, get whichever of these is the closest, and strip, repaint and make your decals. I have a project in waiting for this very procedure as soon as I finish off a few other kits. Anyway, here are the only ones Im aware of:
Guiloy make a 1/10th scale Rossi RSV 250
Minichamps do a limited edition Rossi 250 from 1999, and a Melandri 250 from 2002, both 1/12th. (The detail and finish on these models is fabulous, btw)
Ixo also brought out one in 1/24th - the DePuniet 250 from 2004. (this kit may actually be plastic not die-cast, Im not sure.
These two links will give you more info:
http://www.biante.com.au/find-a-model.htm?submitquicksearch=Search&action=results&keyword=aprilia
http://www.swapmeetmodels.co.uk/guiloy/13611-aprilia-250-rossi.htm
Hope this helps,
Regards,
N