Pay a designer to make them! In this way you will get custom LPs that tailor your needs and you can do additional changes to it over time. Moreover, you might also benefit from the knowledge of the designer. But if you're sure you want to buy just LPs, go to themeforest.net, where you can buy them starting at $10 It's very easy to have a LP accepted by AdWords as long as it's not spammy and you don't sell scam products and services. Good luck!
I would argue with the "very easy" part, although I think Daniel is right for the most part. The issue with Adwords is that you'll find that some industries are very "stable" and very smooth to work with, while some others, you could get suspended for just being in "grey area" industry. So it'll heavily depend on your niche. Make sure the landing page matches exactly the user intent from the query, have a full navigation bar with informative links, get your privacy policy and TOS in place, and you should be good to go.
As Daniel told you you can pay to the designer or company to do the landing page for you. Google is thinking like a human so your landing page should match users queries.
Landing page should be according to your business. For it you should contact a good designer for it.Its good methode to generate leads.
Landing page is help in quality score of your ad. This is very important for users . Unbounce(.)com provide free landing page template and you cna also see their sample of landing page.