Too often vendor provided banner ads are not the best converting, I don't believe they generally provide landing pages, there are outsourced page creators or membership sites with libraries and tools to speed the process of making your own landers.

All offers have landing pages already as otherwise there'd be no site to send affiliate traffic to. But usually the landing pages have lousy optimizations and are generic. You will experience much better results by creating your own landing page that is tailored more specifically to your traffic and target demographics.

Typically the offers will have a website, however if you want a landing page to bridge from the traffic source to the merchants page you will need to create it on your own