|(Updated with news on better Pickup availability) The Retina iPad mini -- which launched earlier today -- is only available through Personal Pickup at US retail stores if it isn't a delivery order, according to an Apple press release. That indicates that US Apple Stores have no walk-in stock, and indeed Personal Pickup orders can't be claimed today. Some shops in other countries, like Italy, do reportedly have Pickup units on shelves.
The situation supports long-standing rumors that Apple will have relatively few Retina Minis available until 2014. US delivery stock appears to be holding out relatively well however, with 16 and 32GB Wi-Fi models shipping in 1 to 3 days, and all other versions going in 5 to 10 days. For contrast, every configuration of the iPad Air is shipping in 5 to 7 days.
Update: Some stores, such as ones in New York City, have been showing same-day Pickup availability for Wi-Fi models.