So far only Sony ( as far as i know ) Have produced a solid state "card" reader head unit. And its only compatible with "Sticks".
That leave you with few other options...
1) An MP3 CD based unit
2) A HardDisk Based Unit - V pricy and reliability is unproven
3) Link you MP3 Player via a suitable input on your/a new head unit
Hope thats of some use.
G