Try Black Hills Central Reservations. They do the whole Black Hills area.

1-800-529-0105

And heres a link that might help:

http://www.sturgis.com/lodging.html

If worse comes to worse, there's always the Buffalo Chip. Real Hard Core camping, but they do have showers. Tough to get any sleep.

If you go early on there may be some rooms. The end of the rally usually has everything booked up for 100+ miles in any direction.

Holiday Inn in Spearfish was charging $350.00 a night last year for a room with two beds for 2 people.

Mark