I was just listening to the Star Wars Action News podcast's Hasbro Q and A (about the 19 minute mark), and one of their questions was about the complaints of the UBPs for 2008 (including the TRU Lars pack) and if the compaints would influence any future releases. Hasbro mentioned costing out the sets has become difficult, and that although the Christophsis pack was "wildly successful", they wouldn't be continuing this line in 2009 and beyond due to costing issues. It may just be Hasbro speak, since they're often quite sneaky with the Target holiday exclusives, but it could be the end of UBPs at retail. I don't know about nationwide, but I didn't seem to have much trouble finding any of the three (Sarlacc, CW, or Lars Homestead) although I only picked up the Sarlacc one personally. I think one of our local Targets may still have one or two of theirs out, and I know that TRU has some Lars Homesteads.
I suppose it could be possible that Hasbro has seen that big vehicles (at least in the $100 range) do just as well as these packs during the holidays, and maybe that's the route we'll see from now on. Anyways, just wanted to pass it along.