How about the Kruse Auction in Auburn, IN (home of the Duesenberg)? Although it's an auction, it's a show too (if you're not buying). I think attendance is close to 200K. They have booths for vendors.
AUBURN SPRING 2009 COLLECTOR CAR AUCTION
18th Annual Auburn Spring Motorfair. The Auburn Motorfair is one of the premier annual auction events, featuring 1,000 outstanding collector cars in the Auction, swap meet, and car corral. This event is held at the 480 acre Kruse Auction Park. Last year we set a new sales record. Join this fantastic event by calling <?XML:NAMESPACE PREFIX = SKYPE /><SKYPE:SPAN onmouseup="javascript:skype_tb_imgOnOff(this,1,'20',true,16,'',0);return skype_tb_stopEvents();" class=skype_tb_injection onmousedown="javascript:skype_tb_imgOnOff(this,2,'20',true,16,'',0);return skype_tb_stopEvents();" id=softomate_highlight_20 onmouseover="javascript:skype_tb_imgOnOff(this,1,'20',true,16,'',0);" title="Call this phone number in United States of America with Skype: +18009684444" onclick="javascript:skype_tb_doRunCMD('call','20',null,0);return skype_tb_stopEvents();" onmouseout="javascript:skype_tb_imgOnOff(this,0,'20',true,16,'',0);" skypeid="20" skypeaction="call" durex="370" context="800-968-4444" IamRTL="0"><SKYPE:SPAN onmouseup="javascript:doSkypeFlag(this,'20',1,1,16,0);return skype_tb_stopEvents();" class=skype_tb_imgA onmousedown="javascript:doSkypeFlag(this,'20',2,1,16,0);return skype_tb_stopEvents();" id=skype_tb_droppart_20 onmouseover="javascript:doSkypeFlag(this,'20',1,1,16,0);" title="Skype actions" style="BACKGROUND-IMAGE: url(file://C:/DOCUME~1/Mark/LOCALS~1/Temp/__SkypeIEToolbar_Cache/e70d95847a8f5723cfca6b3fd9946506/static/inactive_a.compat.flex.w16.gif)" onclick="javascript:skype_tb_SwitchDrop(this,'20','sms=0');return skype_tb_stopEvents();" onmouseout="javascript:doSkypeFlag(this,'20',0,1,16,0);" skypeid="20" skypeaction="drop" skypesms="0"><SKYPE:SPAN class=skype_tb_imgFlag id=skype_tb_img_f20 style="BACKGROUND-IMAGE: url(file://C:/DOCUME~1/Mark/LOCALS~1/Temp/__SkypeIEToolbar_Cache/e70d95847a8f5723cfca6b3fd9946506/static/famfamfam/US.gif)"></SKYPE:SPAN></SKYPE:SPAN><SKYPE:SPAN class=skype_tb_imgS id=skype_tb_img_s20 style="BACKGROUND-IMAGE: url(file://C:/DOCUME~1/Mark/LOCALS~1/Temp/__SkypeIEToolbar_Cache/e70d95847a8f5723cfca6b3fd9946506/static/inactive_s.compat.gif)"></SKYPE:SPAN><SKYPE:SPAN class=skype_tb_injectionIn id=skype_tb_text20 style="BACKGROUND-IMAGE: url(file://C:/DOCUME~1/Mark/LOCALS~1/Temp/__SkypeIEToolbar_Cache/e70d95847a8f5723cfca6b3fd9946506/static/inactive_m.compat.gif)"><SKYPE:SPAN class=skype_tb_innerText id=skype_tb_innerText20> 800-968-4444 </SKYPE:SPAN></SKYPE:SPAN><SKYPE:SPAN class=skype_tb_imgR id=skype_tb_img_r20 style="BACKGROUND-IMAGE: url(file://C:/DOCUME~1/Mark/LOCALS~1/Temp/__SkypeIEToolbar_Cache/e70d95847a8f5723cfca6b3fd9946506/static/inactive_r.compat.gif)"></SKYPE:SPAN></SKYPE:SPAN> for more information.
More details here: http://www.greatcarstv.com/news/kruse-auburn-auction-draws-biggest-crowd-ever.html