Enter the title for the made-for-TV movie in Amazon.com's search field. Not all made-for-TV movies are available on DVD--or even VHS--and you need to ascertain whether the one you want is out there. Amazon provides a good starting point. If the title is available, you can sometimes purchase it from Amazon immediately, or check their affiliated stores to see if a copy is available through them.
Check local stores for a copy of the made-for-TV movie. If it has been released but is not readily available, you may be able to find a copy nearby. Big chains, such as Best Buy and Target, usually are not ideal in these circumstances (although they are good sources for recent made-for-TV movies). A better option is a local mom-and-pop store--especially one that buys and sells used DVDs--or a rental chain, such as Blockbuster, which often sells excess used copies of DVDs.
Visit eBay. Not only can you find someone willing to sell you a DVD of your made-for-TV movie, but you may come across a DVD-R or VHS copy of a movie that has not been officially released. You may have to pay more if it is a hard-to-find movie--and the quality may not be ideal--but if it is rare enough, this avenue may be the only way to obtain a copy.
Check swap meets, flea markets and garage sales in your area. This serves as a last-ditch effort if your made-for-TV movie absolutely is not available anywhere else. Be prepared for a long search--it may not be out there--but you might also find a VHS or DVD-R copy taped from the movie's original airing. When you do, it will be worth its weight in gold.