Just spoken to Gemma @ Palmersport, and there are two more events so far this year, but not 172 specific.
One is an AMG event (16-Aug), the other is a Jag event (04-Sep). The format of the day is very similar - 3 to 4 hours on-track time, and a ride/drive in an AMG Merc/Jag. Alas, no Clio Cup race car time
Price - £150.
Whos interested in coming? Maybe we could get a few 172s together?