I can trade you an English Ditto, (no black or white yet) so a generation 4 or lower pokemon would be fine. Pokemon Nature affects breeding speed:
Lonely lvl 25
Sassy lvl 22
Bashful lvl 22
Jolly lvl 35
Serious lvl 35
Impish lvl 22
Timid lvl 22
Quiet lvl 22
Jolly lvl 22
And some weak HG SS ditto.PM me What you have to offer, and what you would like.