Cut the tree yourself. You are better off with a fake tree than one of the long dead pre-cut trees at Walmart or at a Christmas tree lot. Those trees were cut 1-2 weeks earlier and probably trucked half-way across the country before you even see it. At that point it is good for tinder, and little else.
When you get home, make a fresh cut on the trunk and immediately put the tree in water. This is the key step. The sap starts to dry out and harden in the truck the instant you cut it. If you aren't ready to put the tree in the stand then put it in a bucket of water. When you move it to the stand get it set up and get some water into the stand ASAP.
Keep it watered. Our tree, which I cut 7 days ago, is still sucking down over a gallon a day. It's starting to slow down, but it will still be green and holding onto it's needles at Christmas, which is all that really matters.
That's it. Cut it yourself, make a fresh cut when you get home, and keep it in water. It's not rocket science.