As I recall, some models of Thorens turntables used to have 78, 45, and 33 rpm speeds. One model that I know of with 78 rpm speed is the Thorens TD-190, but there may be other ones that better meet your needs. Jerry Raskin's "Needle Doctor" carries this model. For more info, go to this link: http://www.needledoctor.com/s.nl;jsessionid=ac112b1d1f4367b170aea2cd4867b96eaf48ad14f4f6.qQvJq2PEmlnva30P-BbQmkLz-ATzr6Lzn6rzqwTxpQOUc30KaNDNo6XKq6zInRmLa3mP8RbCpR0HoA5Qmh0KbgTNo6XK-kDvrA4Ka3iIqRnvp6iIpAjOp6jynQjM-AbJpgaMa30PbhySb38T8Oexo6XHngbynknvrkLOlQzNp65In0__?sc=2&category=42&it=A&id=846
Some other brands to seriously consider are Rega, Music Hall, and Pro-Ject, all of which build good tables at reasonable prices. Rega, for example, makes a model called the Planar 78, which is built specifically for 78-rpm playback.
You should also check the web sites for Audio Advisor and Music Direct to see what they offer.