Where can I find a compact/ultra 7 speed freewheel?
Found a few sources by searching on "compact 7-speed freewheel" – here is what Sheldon Brown / Harris Cyclery has. The claim is that they will work, perhaps with the addition of a thin washer or two if the clearance is tight around your dropouts. The appear to have new (or maybe NOS) Sunrace FW760 (13-25), and Shimano FW722 (13-28), and a FW723 (14-34) freewheels in stock.

Nashbar has a 13-24 and a 13-32. It appears that Amazon has some sellers with some as well.

Hillary Stone in the UK also has some, both NOS and used.