It's been a few months since the announcement of the 20GB discontinuation, and during the announcement it said that there was no final shipments. It would just ride out what was on the shelves already. The final shipment could have been weeks prior to the confirmation of its discontinuation, so the shelves were almost barren at that time, must less now.
Honestly, the likelyhood of a PS3 20GB in a store outlet near you (since must be purchased in your state), is totally improbable. Unless you bought a 20GB in the last week, I'd challenge you to find one, somewhere.... I'd almost be willing to put money on it.
However, there isn't anything on the site stating the 20GB isn't apart of this order, but they do know it's been discontinued for some time. My thoughts are out of what movie order forms they received, I'd be willing to bet that seeing a 20GB receipt, would raise some type of flag to have that order reviewed and/or validated. I'm sure they don't have all the man power or desire to validate much, but a recent purchase of a discontinued product, would warrant it, in my book.