I can't seem to find GPO at my local reseller: B&H Photo. I only mention because:
1. They sell Sibelius/Finale versions of same. but not the general GPO, and 2. It's a HUGE retailer. Mostly for visual stuff, but it seems like a good idea to have a retail presence there (of course, my reasons are somewhat selfish: I'd like to buy it locally because it's hard for me to get home deliveries).