When you want to find free expired domain names, there are two ways to act, either you have a minimum of means and you use paid tools, or you start and you have time but no means.
We will see both options.

Paid tools to find expired domain names !

There are many tools to find expired domain names, but I will present only two of them, probably the most efficient.

Find expired domain names with Scrapebox !

Scrapebox is an all-purpose tool for SEOs. If at the beginning it was a tool that was intended to scrape Google, very quickly many features were added and it has become today a real Swiss army knife for SEO. The tool offers among other things a plugin “Expired domain finder” that will allow you to browse several sites to find links pointing to expired domain names. The tool allows different settings such as the number of threads (the higher the number, the faster the software will scrape, provided your computer and your connection holds up), but also the depth at which you want to scrape (the higher the number, the more sites you are likely to find, but the more time you will spend scraping). You can download the Scrapebox software here (and the module directly inside the software)

Find old domain names with Domain Ronin !

This software is specialized and only finds expired domain names, but it does it at high speed. As a comparison, Domain Ronin scrapes about 100 to 150 times faster than Scrapebox, for the same configuration (computer and connection). The operation of the software is very simple: you enter the sites you want to scrape, customize the depth and number of threads, and a few minutes later you will have hundreds of domain names available, and icing on the cake, you will even have the main metrics of the domain names (e.g. TF and CF), without having to have an account or credit with these services. So in just a few minutes you can easily have hundreds of expired domain names, and on top of that you will be able to choose them extremely quickly. You can download Domain Ronin here.

Free tool to find old expired domain names !

Finding expired domain names for free is possible but it often requires a lot of time. First of all you can use online services like brokenlinkcheck.com This type of service will find broken links directly online, however it will scrap very slowly, and above all it will be limited to 3000 pages.
This solution should therefore only be used for small sites, and when you are on the go.

Another solution is to use Xenu to find old domain names !

If the basic purpose of this software is to detect problems on sites such as heavy images, 404 pages, etc., it also allows you to find expired domain names if you divert its primary use.
The principle is simple: you are going to grind a site, and extract all the external links that stand out as being in “no such host”. If this solution works and is not limited in terms of the number of pages visited, it remains on the other hand very long to scrap, and must therefore be reserved for the most modest budgets.