I usually download the product I want directly from Microsoft, when purchasing it, and then have them snailmail me a copy of the disk (incase program crashes) and you don’t even have to leave the house, also there is usually a “free” period to try out the software to make sure you really want that, you will never get that at a store, same with Adobe.
Good luck.

So long as they are on real CDs and contain a license key, they can be purchased on eBay (so pretty much anywhere). Your local computer store may also have some copies available.