Log into WinCustomize forums. Look at upper left just below the Welcome tonygreg1. Click on My Account and then on the far right Registrations. Everything should show up there.
You should have also received an email with links to your purchases.
If this doesn't help you find you Premium Desktops then send an email to sales@stardock.com and give them the information you have on your purchase. You can also reference this thread in your email.