I'm not aware of any asset search feature in the existing image selectors - though it sounds like a nice feature request that you should direct to XMPie...
The uStore DUC (dial user control) - is the object on the customization step which enables the user to enter text/select a date/select an image etc - is a plugin object, so you are able to create custom DUCs for different purposes. This gives you an opportunity to create the exact functionality that you want.